Contains the answers to the questions we’re most often asked. Use the selection below to narrow you search.

• All my data lines run inside the building, why do I need to protect them?

  Even though all data lines stay within the building, communication interfaces are still susceptible to damage. There are two reasons for this. 1. Induced voltages from a nearby lightning strike when control/communications lines run near electrical power wires, metal in the building structure, or near lightning rod ground leads. 2. Differences in AC power voltage references between two devices connected together by control/communication lines. When an event, such as a nearby lightning strike, migrates in on the AC power, individual equipment within the building can see large voltage reference differences. When these devices are connected together by low voltage control/communication lines, the control/communication lines try to equalize the difference, thus causing damage to the interface chips.

• All standard MTL surge products have a 10 year warranty. What does MTL mean when they say this is a 10 year “no fuss” warranty?

  Simply stated the 10 year “no fuss” warranty means that if the product fails within the 10 year period it will be replaced. This warranty includes damage for lightning or from utility power faults. This means that you can be assured that you will not have to purchase another suppressor for this application for at least 10 years. This warranty goes well beyond most other competitors who only warrant their products from failures due to their materials or workmanship. Most do not cover failures due to lightning or utility power faults.

• Answers to Frequently asked questions on Azonix could be found below

  Link to Azonix FAQ

• Answers to Frequently asked questions on Gas Analysers could be found below:

  Link to HiTec FAQ

• Are MTL backplanes SIL certified?

  No, once again these are regarded as ‘wiring components’ in a similar manner to terminal blocks.

• Are MTL barriers SIL certified?

  In the context of ‘functional safety’, simple shunt-diode zener barriers do not perform a safety function and are regarded as just ‘wiring components’. Thus the reliability in terms of the MTBF figures is all that is taken into consideration for the safety loop. The more complex or ‘active’ zener barriers, such as the MTL7706+ or the MTL774x models, will be considered for their use in functional safety applications at a later date.

• Are the Annunciators suitable for use in harsh environments?

  RTK/ MTL annunciators are provided with optical isolation for all of the control inputs as standard. (signal & pushbutton inputs). They are are fully EMC compliant. A high percentage of our annunciators have been in service for many years in harsh environments including offshore platforms, petrochemical plants, nuclear plants, power stations and sub-stations.

• Aren’t Wireless LANs insecure?

  Saying a wireless LAN is insecure is like complaining a car, with central locking, an immobiliser and alarm is insecure when it is unlocked.  All Wireless Access points support some degree of security, most people do not turn this security on, and as such Wireless technology was perceived as being insecure.

  Some of the common security steps include: -

  Physical Security:  By using appropriate antennas it is possible to restrict the propagation of the radio waves as needed. So if a link is to be based in a building, using a patch antenna attached to the wall will severely restrict the amount of radio waves that propagate through that wall and so the ability to pick up this information. Failure to address physical security could be likened to hanging a network cable out of a window.

  MAC Layer security: The 802.11 standard specifies two main technologies to secure the MAC layer of the wireless network.

  WEP: Wired Equivalent Privacy uses keys to encrypt the data that is being transmitted, without the appropriate key the data is unreadable to anyone receiving the data.  WEP is a “crackable” standard, this means that using appropriate software, and a few days of monitoring the wireless network it is possible to gain the key and therefore decrypt the data.

  WPA: WiFi Protected Access has been introduced by the WiFi alliance in order to provide increased security until the 802.11 standard ratifies a more secure method than WEP, it once again uses keys to encrypt the data being transmitted, but in this case the keys are constantly changed to prevent them from being recovered using software.  WPA is currently regarded as “uncrackable”.

  VPN: Virtual Private Networks are a technology that is used to allow secure communications across public networks (primarily the Internet).  These same technologies can also be used to secure data being transmitted across wireless mediums.  Once again these devices encrypt data so that without the correct keys the data is unreadable, there are various technologies used including DES, 3DES and AES.  The American Military regard 3DES (pronounced triple DES) as secure.

  Using a combination of these technologies it is possible to restrict how can pick up your signal, when they have intercepted it they have to decrypt the MAC layer, and once this has been completed they have to decrypt the VPN layer, this level of security far exceeds the security used on cabled systems and makes other means of gathering the information (such as staff corruption) much more attractive and likely.

   

   

• As MTL are a certified FSM company can they provide guidance in developing a SIL loop?

  No, the design of the safety function is the responsibility of the user not the vendor. MTL provide the information needed to select, install, operate and maintain our products in the Safety Manual.

• Can a manufacturer such as MTL state their products are “SIL 3 certified” rather than “suitable for use in a SIL 2 system”?

  The steps required to define, design, verify, install and commission safety functions are given in the life cycle contained within the standards. For the process industries the IEC 61511 standard is the sector specific standard to follow and it would be foolish to attempt any activity for a safety function without reference to this standard.

• Can an individual product (i.e. Isolator) be SIL rated?

  Products (components) must be suitable for use in a safety loop (function) up to the integrity level that the loop is to achieve. Remember that it is the complete safety loop or safety function that has a Safety Integrity Level and not a particular component. Each component, by itself, does not perform a safety function – it is the complete chain of components operating together that implement the safety function designed to mitigate the identified risk.

• Can I replace a SIL2 rated isolator from one supplier with another supplier product with the same SIL rating and safety parameters?

  Essentially yes, but once you have satisfied that the operational parameters, the intrinsic safety parameters and the functional safety parameters are compatible, then updated the loop design records and documents to support the change. This must then be verified by the safety system designer with the appropriate level of competence. Remember also to consider the proof-test requirements for the new component compared to the old one to ensure the PFD is not impaired. In similar vein to the requirements for maintaining intrinsic safety loops, then any change likely to affect the functional safety of a loop must be adequately assessed, documented and approved.

• Can I use a field device that is not FISCO certified with the MTL FISCO power supplies?

  Yes. Field devices that are only certified to the entity profile can be used with the MTL FISCO power supplies by including a spur connector in the connection to that device. The entity spur connector is usually located in the fieldbus junction box.

• Can I use MTL5000 series for safe area applications ?

  When using MTL5000 series modules in safe area applications, it is important to change the "blue" connectors for appropriate "grey" connectors, labelled correctly for safe area use. For such applications, two new safe area connectors are now available, as detailed below.
  
  Part no.
  SAF1-3 available as standard accessory
  SAF4-6 available as standard accessory

• Can managed and unmanaged switches could be connected together ?

  Yes, but for best system optimisation & diagnostics, the utilisation of managed switches throughout
  is advised.

• Can the CMP software / Tofino routing through another server?

  Yes, CMP and Tofino need ports 6689 or 65000 open to communicate through a Firewall

   

• Can the existing 932x-SC Spur Connectors be used to connect to 'Entity' certfied fieldbus devices, and devices in Zone 0 hazardous areas?

  Yes, these can be used on Redundant FISCO segment in exactly the same way as for simplex.

• Can the modules be 'hot-swapped' to allow replacement of failed modules without losing power or communications?

  Yes. The power supply and Supply Arbitration Modules may be easily ‘hot swapped’ without powering down the system, and without causing loss of power or communications.

• Can you deploy Tofinos in a redundant network?

  YES - Generally Tofino can be used on redundant networks based on systems like Spanning Tree Protocol (STP), Fault Tolerant Ethernet (FTE) and others straight out of the box.

• Does removing or repowering a MTL4841 affect the analogue signals?

  The MTL4841 and MTL4842 can both be removed or the MTL4841 re-powered without interfering with the analogue 4-20mA signal.

• Does the Redundant FISCO power supply work with existing Intrinsically Safe Megablock wiring hubs, or do they need to be different?

  Redundant FISCO works with MTL’s existing range of IS Megablocks (types F245 – F271).

• Doesn't the FISCO standard say that there should only be one source of power in a FISCO network, making it impossible to have redundant power supplies?

  No. This clause in the IEC60079-27 standard is intended to mean that the maximum values of Uo, Io and Po for the power supply must not be exceeded on any segment, and that the power must be connected at only one point on the bus. MTL’s solution complies with both these requirements because it provides power onto the segment at only one point (at the power supply terminals), and the Uo, Io and Po values for the redundant output will be certified to comply with the maximum values specified for FISCO.

• Even if the incoming phone lines are protected do I need additional protect the telephone lines?

  The protection the Phone Company provides is there mainly for personal safety to prevent lightning from migrating in on their wires and causing personal injury. It provides little protection for sensitive electronic communications equipment. It provides primary protection but does not eliminate the need for secondary protection at the equipment.

• How can I access MTL Partner portal?

  MTL offers its key customers and partners access to its customer portal. Customer portal could be accessed via the MTL Extranet. This requires registration and the registration process could take up to 3 working days.

   

  Log in to MTL Extranet

   

• How could a PLC using MODBUS/TCP possibly be a security risk to my control system?

  MODBUS has no authentication and may be easily spoofed so any MODBUS devices controlled/monitored by Windows PCs which may be compromised.

• How do I initiate an RMA ( Return Material Authorisation) or Product Return?

  For MTL Intrinsic Safety, Fieldbus, Industrial Ethernet and Industrial Wireless Products please contact your local MTL sales office or representative.

  Contact us
  

  For Gecma / HMI products please indicate and RMA via RMA Portal.

   

   

• How do I preform a factory reset on an MTL9211-ET Tofino hardware unit?

  Power the Tofino off, hold down the large mode button while you power it up, keep holding until all four LEDs blink twice. It may take as long as 2 minutes. Once they blink you can release the button and the Tofino has reset.

   

• How do the “simple apparatus” rules relate to the current “well defined” parameters?

  The relevant clause in the standard IEC 60079-11 is 5.4, and states in section b) “sources of stored energy with well defined parameters, for example capacitors or inductors, whose values shall be considered when determining the overall safety of the system”.
  
  This was introduced because the 20 microjoule figure of the previous definition is difficult to defend. Adding 20 microjoules to a IIC system, which may already be on the acceptable limit more than removes the safety factor. Another problem is that a thermocouple delivering 10 mV and 1 mA generates 20 microjoules in 2 seconds, hence the energy figure should have had a time assosciated with it.
  
  The new clause does allow a further degree of freedom, particularly if IIB and IIA gases are being considered. The analysis should assume that all the capacitors and inductors within an apparatus are added together and considered as appearing directly across the terminals of the apparatus.The draft system standard requires that the sum of ALL the relevant parameters of ALL simple apparatus within an IS circuit shall be taken into account. Implicit in the same document is that a justification of why a piece of apparatus is considered as “simple” should be included in the safety documentation. The redrafted clause does give greater flexibility,but is not significantly different from considering the capacitance and inductance of cables.
  
  The clause does allow the construction of some complex circuits, but whoever makes the claim of “simple apparatus” must document the analysis, sign it, and accept responsibility for it. It is a usefull solution to the occasional difficult short term problem. However, if a product is to be sold in significant numbers it will almost certainly have to be certified. Care should be taken when analysing simple apparatus to apply the full clause including the restrictions of the second part. This means that any complex apparatus can only be analysed by someone who is familiar with the whole standard and is knowledgeable in the field of intrinsic safety. Such persons are VERY RARE!

• I am applying 24Vdc to an MTL7787+ to drive a 24V relay coil but it doesn't work. Why not?

  You are not taking into account the resistance of the barrier.

  For optimum efficiency, the resistance of the relay coil should be the same as the resistance of the barrier (i.e. "matched"). However, this means that you will get only half the supply voltage (12V) at the relay coil.
  You should therefore use, for example, a 12V, 400 ohm relay coil.
  
  Rt (Total resistance) = Rb (Resistance of barrier) + Rc (Resistance of coil)
  
  Isupply (Current flowing in circuit) = Vsupply / Rt
  
  Vc (Voltage at coil) = Rc x  Isupply.
  
  Alternatively you could use an MTL774X product which provides simple "volt-free" contacts in the safe area to operate the relay coil.

• I cannot get an output from the SAFE side of a MTL5032. What is the problem?

  The output terminals 11 and 12 are not powered so you will have to provide the voltage. Below is a typical circuit showing a 24 VDC supply.

• I have a control cabinet and some transmitters I want to protect. If I protect the power and the signal lines at the control cabinet end will the transmitters be protected?

  No, if surge current is present on the signal lines it will be seen on both ends of the lines. Properly protecting the power and signal lines at the control cabinet end will only protect the control cabinet. Surge protection must also be installed at the transmitters if they are to be protected.

• I have product which I would like to use in a SIL loop; as MTL are a certified FSM company can they provide certification for my product?

  No. We are only responsible for our own products.

• If a "hacker" manages to obtain a copy of the CMP (Central Management Platform) software and connect it to my network, could he take over my Tofino?

  ABSOLUTELY NOT - Each CMP database has a unique random key. The first time a CMP establishes a connection to new Tofino appliance, it uploads its random key to that Tofino. From then on that Tofino can only communicate with the CMP that owns the key.

• If a Tofino appliance doesn’t have an IP address, how can I communicate to it over an IP network?

  The Tofino uses a patent-pending technology to “borrow” IP addresses of the devices that it will be protecting for its configuration and event messages. This does not impact the devices being protected in any way, but it makes the Tofino almost impossible for hackers to detect.

• Is a defense-in-depth strategy important for all control systems or is it just needed for very critical safety systems?

  A defense-in-depth strategy is needed for all control systems. The North American Electrical Reliability Council (NERC) notes that poor defense in depth design is the second most common security vulnerability in modern control systems.

   

• Is full protection going to be too expensive?

  Full protection is one of the most inexpensive insurance policies you can buy. The cost of system inavailability is far more expensive than proper protection. One major surge event in a ten-year period far outweighs the cost of protection.

• Is it true that if a safety loop is designed as SIL2 then all the individual components in that loop should be rate to be used in SIL2 as well?

  This is the simplest way to achieve the goal but remember that duplication or triplication of the signal paths is often used to reach the target too. Thus components with lower ratings are employed in parallel to implement the overall safety function, which reduces the demands upon the individual items.

• Is lightning my only concern when I am considering surge protection?

  No, actually the majority of premature equipment failures from surge impulses are caused by much lesser events than direct lightning strikes. Small electrical impulses caused from other users on our same power grid, utility grid switching, electrical motors, and many other sources cause the majority of surge related failures in today’s electronic equipment. These smaller impulses will degrade the minute internal junctions inside IC chips over time and cause premature failure.

• Is the change-over to redundant FISCO 'bumpless' ?

  Yes. Interruption of fieldbus communications is momentary, and is accommodated by the re-transmission mechanism that is implicit in the Foundation fieldbus protocol. There will therefore be no loss of control, and the plant operator will observe no loss of data.

• Most MTL surge protection devices for signal and communication devices indicate that they have a hybrid circuit. What is the advantage of the hybrid in the MTL devices?

  This allows our surge protection devices to have a high surge current capacity (so they are not easily damaged from nearby lightning strikes) and precise limiting voltage characteristics (so the voltage seen at your equipment has been limited to a very low level).

• MTL 55xx series of products are certified for use in hazardous areas so could they all be allowed to be used in safety systems?

  No. With our isolator products Intrinsic Safety relates to the prevention of explosion by constraining the electrical energy passed into the hazardous area under all conditions, both in normal operation and including when faults are present. The risks that are mitigated by the safety functions are concerned with the process under control and maintaining this in a safe state.

• MTL show the Safety Description of the zener barriers on the data sheet, but it only shows voltage, resistance and current. A number of field equipment certificates also show power. Do I have to confirm that the barrier has a value for power that is acceptable and how can I check this?

  Yes, you have to ensure that the barrier power value is not greater than the power value given for the field equipment.
  The maximum power transfer between the safe area and the field takes place when the impedance of the source is equal to the impedance of the load. This is called the Matched Power.
  This is the worst case condition and so this is used to calculate the power output from a barrier. Under these conditions the power can be expressed as:-
  
  Matched Power = Voc x Isc / 4 (W)
  
  For a typical 24V dc barrier, MTL7728+, with safety description 28v, 93mA.
  
  28  x  0.093  =  2.604
  
  2.604 / 4  =  0.651W
  
  However the power value for each channel of a barrier is provided in the Maximum Cable Parameters table for each barrier series.

• MTL4041B - What is the input resistance at hazardous area pins 5 and 6?

  Less than 50 ohms, and typically 30 ohms.

• MTL4073 - What is the hazardous input resistance and safe area output impedance ?

  10V/m with 1kHz sine wave modulation to 80% of the carrier level are the minimum RF levels specified in the Generic Immunity Standard for Industrial Environments EN50082 part 2.

• MTL5000 Series - What crimp ferrules are available for 1.5mm2 wire ?

  We have not been able to locate any ferrules with 12mm length metal tubes for 1.5mm2 wire in any supplier catalogues (unless you have seen any?!).
  We recommend you use the following 18mm metal tube length ferrules:-
  PKE1518 (1.5mm2) and PKE2518 (2.5mm2) from Cembre, and cut them to 12mm length after crimping.

• MTL5042; what is the safety description for terminals 1 and 3?

  Non-energy storing apparatus can be connected between terminals 1 and 3.
  
  See under 'Safety description, Terminals 1 to 3' in the MTL5042 data specification.
  
  Terminals 1 and 3 can be connected into an IS loop as long as the open circuit voltage <28 V. Therefore, determine the output safety parameters for the field device and ensure they comply with this voltage.There are no specific cable parameter figures provided for this combination of terminals on that certificate. The only reference to cable parameters on the certificate is on page 3:-
  
  "The capacitance and either the inductance or the inductance to resistance ratio (L/R) of the load connected to the output terminals must not exceed the following values: Group IIC - Co < 0.13uF,  Io < 4.2mH or L/R < 55uH/ohm"

• MTL55xx isolator datasheet stats that it could be used in SIL3 rated safety function loops so can this be used in SIL2 rated safety function loops?

  Look at the definitions of the safety integrity levels. If a component has been assessed as suitable for use up to SIL3 then it can also be used in loops that need to achieve SIL2 or SIL1.

• My control system is never connected to the Internet. Am I still at risk from cyber incidents?

  Absolutely - most attacks enter the system from either the business network or through secondary pathways such as infected laptops, USB keys, remote access over Virtual Private Networks (VPNs) or modems.

• My control system is separated from the business network with a firewall. Do I still need additional security?

  Many attacks come through secondary pathways such as infected laptops, remote access over VPNs, and modems that will completely bypass the firewall. To address this, the critical devices inside the control system firewall should be given additional layers of protection (eg: office PCs have personal firewalls and anti-virus software). This is known as a defense-in-depth strategy

• My DCS vendor says that their protocol has authentication or has been security-certified. Do I still need a Tofino?

  If the DCS only uses that authenticated protocol and that protocol has been security tested by a certification service such as MUSIC or Idaho National Labs, then the protocol is probably secure. However, many products also communicate using older un-authenticated protocols such as Ethernet/IP, MODBUS, HTTP or telnet.

• My transmitter only cost $1,000.00 so why should I consider spending $200.00 to protect it from surge events?

  There are many things to consider when you are justifying the cost to protect. More important than the actual replacement cost of the transmitter is the loss of the function of the transmitter. Usually the functional loss associated with the loss of the transmitter for a period of time is the main justification in providing protection. Another justification to consider is the labor cost and travel cost that could be incurred in the repair.

   

• On the MTL AC mains panels surge protection cut sheets they indicate the product is for a 120/240V single phase (split phase) system, i.e. ZD16100 or ZM11200. Does this mean that the product will work with either a 120V or a 240V single phase mains service?

  No, a 120/240V single phase (split phase) is a unique electrical service mainly seen only in the Americas and Japan. The 120/240V single phase (split phase) products have two separate 120V legs a neutral and a ground. Products designed for this service will not work on 230V or 240V single phase systems. Products designed for 120/240V single phase (split phase) applications would be immediately damaged when connected to 230V or 240V single phase services.

• Our equipment is connected to a UPS, do we still need surge protection?

  UPS systems play a very important part in an overall power protection plan. They are designed to provide good clean uninterruptible power to critical equipment. They provide no protection for the communication and control lines found in today’s network type environments. They also do not normally provide AC power protection to the many nodes connected within the network. The surge protection elements found within even a very large UPS is very small in comparison to stand-alone SPD’s. Normally around 25 to 40kA. In comparison, our smallest AC entrance protector is 70kA and our largest is 600kA.

• Should CMP (Central Management Platform) be always online? What happens if CMP is down? Will network security be breached?

  If the CMP is shut down there is no risk to security whatsoever. We suggest that the Tofino CMP is left online at all times so it can collect events from Tofinos in the field and provide alarms to the operator, however this is strictly optional.

• Should I install a separate ground for the surge protection device?

  No, the surge suppressor should be grounded to the same ground reference as the equipment it is protecting.

• We are based in an area with very little lightning, why do we need surge protection?

  Many areas of the world do not experience as much lightning related problems as others. As much as companies today depend on their control and network systems, the system availability has become paramount. For most companies, a single surge related incident in a ten-year period, which causes the loss of system availability, would more than pay for proper protection.

• We have good grounding, do we still need surge protection?

  A good ground is important for surge protection devices (SPD) to work properly. AC power SPD’s are designed to divert surge current to ground by providing the least resistive path. Without surge protection on the AC power, the surge current will look for other paths to a good ground. In many cases this path is found through electric/electronic equipment. Once the dielectric strength of the components in electronic equipment has been surpassed large currents begin to flow through the sensitive electronics thus causing failure.

• We’ve never had any problems with surges, why do we need surge protection?

  There are not many areas of the world today that do not experience surge-related incidents. Lightning is only one of the many causes of transient surge related problems. Today’s modern electronic equipment is much smaller, much faster, and much more susceptible to transient related problems than was the last generation of equipment. The sheer number of control and communication devices interlinked together in today’s networks make their susceptibility many times greater. These are new problems that were not nearly as frequent with previous generations of control equipment.

• What allowance do I make for field device inrush current when designing a FISCO/FNICO segment?

  When designing a segment with a FISCO or FNICO power supply no allowance needs to be made for inrush current. The IEC61158-2 fieldbus standard allows fieldbus devices to draw up to 20mA above their design current for up to 20ms on start up.
  
  The current limit of the FISCO and FNICO power supplies is at least 20mA above the design current used for segment calculations. This means that if a device is disconnected from a fully loaded segment; on reconnection, it can briefly draw up to 20mA above the design current, without affecting the normal operation of the segment.
  
  The FISCO and FNICO power supplies have a soft start feature to ensure the fieldbus segment starts up. For example for a segment with 16 x 15mA devices powered by a 9122-IS IIB FISCO power supply, the segment will normally require 240mA which is less than 265mA 9122-IS design current. On start up the segment could have an initial current draw requirement of 240mA + 16 x 20mA in rush current or 560mA. The 9122-IS will supply at least 285mA for up to 1 sec, which is long enough to power up all the field devices. In the MTL fieldbus test laboratory we have proven that the segment will start up when fully loaded with devices with the highest in rush currents, confirming that with MTL power supplies no additional allowance should be made for in rush current in segment calculatlions.

• What allowance do I need to make for the fieldbus signal when designing a segment?

  No allowance needs to be made for the fieldbus signal if the segment uses a FISCO or FNICO power supply. As the fieldbus signal is symmetrical, the terminators act as a current source/sink for the fieldbus signal, so no extra current is drawn from the power supply.

• What allowance do I need to make if using a SpurGuarded™ Megablock with a FISCO power supply?

  The F240-F259 range of Relcom SpurGuard™ed Megablocks are designed for IS applications and are ideal for providing wiring connections on a FISCO segment. The F251 8-way Megablock normally draws 3.5mA plus the current for any devices connected. In the event ot a device having a short circuit, that device will now draw a maximum of 42mA instead of its normal current (e.g. 15mA).
  
  For example, consider a segment with sixteen 15mA devices connected via two F251 8 way Megablocks powered by a 9122-IS IIB FISCO power supply. The segment will normally require (16 x 15 + 2 x 3.5 =) 247mA which is less than the 265mA 9122-IS design current.
  
  If a single spur has a short cicuit, the current consumption will be 247 + 42 –15mA = 274mA, which is still less than the 285mA current limit of the 9122-IS, so this segment design is OK.
  
  Additionally, you will need to check that the voltage at the devices will always be greater than 9V. Some designers use a minimum of 10V at a device to provide some margin.
  
  An MTL-Relcom segment calculator is available which will automatically complete all these calculations for you. With typical type A cable (0.8 sq.mm, 44 ohm/loop km) and all devices at the end of the trunk connected by 30m spurs the maximum permitted trunk length would be 330m. Under the same conditions but with 1.5 sq.mm, 22 ohm/loop km cable, the maximum permitted trunk length would be 660m.
  
  On the few occasions when longer trunks are required, either fewer field devices could be connected to the segment or, alternatively, the FISCO power supply could be mounted in a Zone 2 hazardous area, close to the field devices.

• What are the maximum interconnection cable lengths?

  The maximum recommended length of 20 way HART ribbon cable between the BPHM64 backplane and the HART connection unit or IS backplane is 6 metres or 20 feet. Flat ribbon cables should not be taken outside the cabinet as they are not robust and susceptible to noise. Ground loops may also be an issue. If possible, locate the HART mux units close to the take-off points. For larger distances use more than one BPHM64 with MTL4841 modules fitted and link via the RS485 bus.
  
  The maximum length of 10 way interface bus cable between a single MTL4841 communications module and up to 16 MTL4842 HART interface modules / backplanes is 4 metres or 13 feet, (between modules 1 and 16).

• What cable lengths can be supported using Redundant FISCO?

  * - Limited by total segment length

  No. Field devices per segment	Average field device current	Trunk cable cross-section	Total segment current	Spur cable length	Gas Group	Maximum trunk cable length	Total segment length
  6	17mA	1.5mm2 (240 ohms/km loop)	130mA	60m	IIB	1050m	1410m
  8	17mA	1.5mm2 (240 ohms/km loop)	164mA	60m	IIB	831m	1311m
  10	17mA	1.5mm2 (240 ohms/km loop)	198mA	60m	IIB	690m	1290m
  12	17mA	1.5mm2 (240 ohms/km loop)	233mA	60m	IIB	585m	1305m
  5	17mA	1.5mm2 (240 ohms/km loop)	113mA	60m	IIC	700m*	1000m
  5	17mA	1.5mm2 (240 ohms/km loop)	113mA	30m	IIC	700m*	1000m

• What causes the I/P, MTL4045B, DCS output card to 'lock-up'?

  This very rare loop lock-up problem with MTL4045Bs is associated with higher inductance I/P devices (of which there are not many). The short-circuit detect in the MTL4045B triggers a series of events in the I/P, MTL4045B, AO card loop which locks it up. The remedies are either:

  • Insert a resistor (as high a value as possible
  • Change to the MTL4045C

  It is not a simple matter to characterise the specific properties of the I/P devices that cause this problem with the MTL4045B, because it depends on the combination of the inductance and damping properties of the device.
  When testing, try the resistor solution first, but otherwise, if possible, change to the MTL4045C.

• What distance can you cover between two MTL5051s in separate hazardous areas?

  MTL5051 remote signalling baudrate formula - Back-to-back mode across hazardous area.

  Max baudrate = 0.25 / (R x C x L2) or Max. distance = Sq Root ( 0.25 / (R x C x B)) where:

  R = cable resistance [ohms/m]
  C = cable capacitance [Farads/m]
  L = length [m]
  B = baudrate [baud]
  
  So for example, with a 2Km cable of 100pF/m and 40mohm/m:
  Max baudrate = 0.25/(40x10-3.100x10-12.(2000)2) =15,625baud
  
  [Note that this assumes that the cable has 2 cores plus a screen, with the screen used for the Common connection].

• What do the various gas groups mean?

  Gas grouping is a way of arranging the majority of flammable gases according to the energy required to ignite them. Most countries mark all surface industry equipment with the Roman numeral II: the gas groups are then sub-divided into IIA (propane), IIB (ethylene) and IIC (hydrogen) – IIA being the least incendive. The names given in parentheses are representative gases; frequently used to describe the gas group. America and Canada chose to use different group names when marking equipment but, of course, the ignition energy remains the same.

  Test gas & ISA RP12.2 Group IEC Groups SFA 3012 SFA 3004 EN 50 014 American NEC Article 500 Flameproof Group Ignition Energy microJoules Propane IIA D 180 Ethylene IIB C 60 Hydrogen IIC B 20 Acetylene IIC A 20

• What do the various temperature classifications mean?

  Gas-air mixtures can be ignited by contact with hot surfaces; consequently electrical equipment used in hazardous atmospheres is required to be classified according to its maximum surface temperature. From the table below it can be seen, for example, that an item classified as T4 will not exceed a surface temperature of 135°C. These classifications are based upon an ambient temperature of 40°C, unless otherwise specified on the device. If the equipment is to be used in ambient temperatures higher than this, the temperature class must be reassessed.

  Class Maximum surface temperature oC T1 450 T2 300 T3 200 T4 135 T5 100 T6 85

• What do the various zones represent?

  Hazardous area are divided into zones to indicate the probability of a hazardous mixture of gas (or dust) and air being present. The present IEC standard defines the zones as follows:
  	Zone 0:	A place in which an explosive gas-air mixture is continuously present for long periods, > than 10 000 hrs/annum.
  	Zone 1:	A place in which an explosive gas-air mixture is likely to occur in normal operation, >10 and less than 1000 hrs/annum.
  	Zone 2:	A place in which an explosive gas-air mixture is not likely to occur, and if it occurs it will only exist for a short term, <10 hrs/annum.
  	Zone 20:	A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, or for long periods or frequently.
  	Zone 21:	A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally.
  	Zone 22:	A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation, but, if it does occur, will persist for a short period only.

• What do you use as a signal supply voltage with your annunciator range?

  Our annunciator range use a +24VDC signal supply voltage as standard. This is provided via a fused spur within the annunciator and distributed to customer terminals for use as a signal wetting voltage. As an option RTK can supply inputs suitable for use with externally powered 24V, 48V, 125V or 250V signals but the signal supply is provided externally by others.

• What does MTL mean when they say this is a 10 year “no fuss” warranty?

  Simply stated the 10 year “no fuss” warranty means that if the product fails within the 10 year period it will be replaced.  This warranty includes damage for lightning or from utility power faults.  This means that you can be assured that you will not have to purchase another suppressor for this application for at least 10 years. This warranty goes well beyond most other competitors who only warrant their products from failures due to their materials or workmanship.  Most do not cover failures due to lightning or utility power faults.

• What FISCO certified field devices are available today?

  All major automation vendors have committed to FISCO certifying their intrinsically safe field devices. The following manufacturers have a wide range of FISCO certified field devices

  ABB
  Emerson Process Management
  Endress + Hauser
  Flowserve
  Krohne
  Metso
  Vega
  Yokogawa

  
  Infraserv of Frankfurt, Germany carried out fieldbus interoperability testing with 43 field devices from a wide range of manufacturers and reported that 83% were FISCO certified by the end of 2002. More have been certified since then so there is a wide choice of FISCO certified devices available today.

• What is a Safety Integrity Level (SIL)?

  A safety integrity level is one of four levels, each corresponding to a range of target likelihood of failures of a safety function. Note that a safety integrity level is a property of a safety function rather than of a system or any part of a system.

• What is a safety manual?

  For all suppliers of products and equipment used in safety functions who claim compliance with the standard then a safety manual is required. The purpose of the safety manual for compliant items is to document all the information which is required to enable the integration of the item into a safety-related system, or a subsystem or element, in compliance with the requirements of the standard. The selection, installation, operation, and maintenance of the equipment to achieve the safety function are all detailed in the safety manual.

• What is an "IS earth"?

  Protective earthing is a vital part of the safety of almost all electrical systems where potentially explosive gases may constitute a hazard. Correct earthing is important for all protection techniques, including intrinsic safety.
  
  Adequate earthing, though not spelled out in the particular installation codes, is absolutely vital to the safety of all mains-powered electrical equipment, whatever the protection technique. Section 22 of the BS 5345 Part 1 lists no special requirements for the earthing of hazardous area systems but is a convenient cross reference to other documents.
  
  BS 5958: Part 1: 1980, which is a code of practice on the avoidance of static hazards and contains some sound practical advice, should be read as good background information on which to build.
  
  Consider a conventional site with a local distribution transformer and with the neutral star point connected to the standard earth mat. The primary purpose of this mat is to provide an earth return path for any faults that may develop in the distribution system, where the conductivity of the soil may provide a possible current path. Conventionally, each electrical installation provides a return path to the neutral star point in its wiring, via either the cable armour or a specific conductor which is capable of operating its protective network. This is supported by the interconnection of the equipment to the metallic structure which generates a web of structural interconnections to the various electrical equipment return paths. Further support is usually provided by the structure and the antistatic bonds which are normally present. There is nearly always a third parallel path through the soil, but this indeterminate path is not usually relied upon for first line safety connections.
  
  The more probable source of direct invasion of intrinsically safe circiuts is within the safe area shown in Fig. 9.2. The first essential of the dafety earth on the barrier busbar is to provide a return path of low impedance so as to prevent any significant proportion of the faule current entering the hazardous area. This fault current is returned to the neutral star point bond and hence back to the distribution transformer.
  
  The current flowing though the bonding conductor generates a potential difference between the IS earth point at the barriers and the neutral star point. The outside of the field-mounted instrument is bonded to the neutral star point, and the internal circiuts of the instrument are connected to the barrier busbar. The potential difference between IS earth point at the barriers and the neutral star point is therefore transferred to the hazardous area. It is normally safe because this internal circuits are isolated from the instrument housing, but this potential difference should be minimised so that if there is a local insulation failure no danger can arise. The installation conditions of barriers, screened transformers etc. nearly all call for a return path impedance less than 1 ohm. A figure of 0.1 ohm is normally achievable and is more desirable. It is important to remember that the resistance involved is that of the return conductor between points IS earth at the barriers and the neutral star point and the resistance of the earth mat is not important for this purpose. These principals are normally applied within the UK.

• What is difference between Point to Point and Point to Multipoint wirelss connections?

  Point to point describes applications such as connecting two buildings together this is also the scenario described when the term bridging is used. Point to multipoint describes an application where a central point connects to a lot of other points (a single building connecting to multiple buildings, or even multiple clients connecting to the same access point)

   

• What is functional safety assessment and what is involved?

  The objective of the functional safety assessment investigate and arrive at a judgement on the adequacy of the functional safety achieved by the E/E/PE safety-related system(s) or compliant items (e.g. elements/subsystems) based on compliance with the relevant clauses of this standard.
  Functional safety assessment is the critical activity that ensures functional safety has actually been achieved based on compliance with the relevant clauses of this standard. Those carrying out the functional safety assessment shall be competent, shall have adequate independence and shall consider the activities carried out and the outputs obtained during each phase of every lifecycle and judge the extent to which the objectives and requirements of IEC 61508 have been met. See clause 8 of IEC 61508-1 for further details.

• What is Functional Safety?
  • Functional safety is part of the overall safety that depends on a system or equipment operating correctly in response to its inputs.
  • Functional safety is achieved when every specified safety function is carried out and the level of performance required of each safety function is met.
  • Functional safety relies on active systems.
  • An example of functional safety would be the activation of a level switch in a tank containing a flammable liquid, when a potentially dangerous level has been reached, which causes a valve to be closed to prevent further liquid entering the tank and thereby preventing the liquid in the tank from overflowing.
  • Safety achieved by measures that rely on passive systems is not functional safety. A fire resistant door or insulation to withstand high temperatures are measures that are passive in nature and can protect against the same hazards as are sometimes controlled by functional safety concepts but are not instances of functional safety.
  • See also IEC/TR 61508-0 Ed1.0, Functional safety of E/E/PE safety-related systems - Part 0: Functional safety and IEC 61508 for further details.

   

• What is IEC61508?

  IEC 61508 is a 'generic' standard, intended to satisfy the needs of all industry sectors. It is a large document, consisting of seven parts and a total of about 400 pages. Ideally it should be used as the basis for writing more specific (e.g. sector- specific and application-specific) standards, but it is also intended to be used directly where these do not exist. It has become a requirement of many customers, and its principles are perceived as defining much of what is considered to be good safety-management practice.
  The standard consists of seven parts. The first four are 'normative' - i.e. they are mandatory - and the fifth, sixth and seventh are informative - i.e. they provide added information and guidance on the use of the first four.
  

  • Part 1 (General Requirements) defines the activities to be carried out at each stage of the overall safety lifecycle, as well as the requirements for documentation, conformance to the standard, management and safety assessment.
  • Part 2 (Requirements for Electrical/ Electronic/ Programmable Electronic (E/E/PE) Safety-Related Systems) and Part 3 (Software Requirements) interpret the general requirements of Part 1 in the context of hardware and software respectively. They are specific to phase 9 of the overall safety lifecycle, illustrated in Figure 4.
  • Part 4 (Definitions and Abbreviations) gives definitions of the terms used in the standard.
  • Part 5 (Examples of Methods for the Determination of Safety Integrity Levels) gives risk-analysis examples and demonstrates the allocation of safety integrity levels (SILs).
  • Part 6 (Guidelines on the Application of Parts 2 and 3) offers guidance as per its title.
  • Part 7 (Overview of Techniques and Measures) provides brief descriptions of techniques used in safety and software engineering, as well as references to sources of more detailed information about them. In any given application, it is unlikely that the entire standard would be relevant. Thus, an important initial aspect of use is to define the appropriate part(s) and clauses.
• What is included in the Tofino™ Starter Pack?

  Tofino Starter pack (9530-STP CK) consist of : 1x Tofino SA, 1x Central Management Platform (CMP), 1X Secure Asset Management LSM, 1X Firewall LSM.

  Please note starter Pack CMP restricted to managing a maximum of 3 Tofino SAs per facility

  Tofino Starter Pack Datasheet

  Download File

• What is the advantage of installing AC mains protection on the main electrical service entrance panel at my site?

  Without this protection, any large surge events coming on the AC mains utility line will pass on through the service entrance panel and will be seen on all the electrical wiring throughout the site. With the proper protection at the AC mains service entrance the large surge event can be reduced down to a controllable level thus limiting the voltage seen throughout the site.

• What is the difference between the MTL4045B and MTL4045C?

  They are the same except that the MTL4045B has a short-circuit detection circuit on the hazardous side. So an MTL4045B can be thought of as an MTL4045C with a short-circuit detection facility and an MTL4045C; as an MTL4045B without a short-circuit detect facility. Consequently the MTL4045B has a minimum hazardous area load resistance of 90 ohms. This is because the short-circuit detection circuit is guaranteed to detect at <50 ohms and actually starts working marginally at about 70 ohms, so a minimum load resistance of 90 ohms is specified to prevent lower resistance I/P devices from being interpreted as short-circuits. This gives the following line fault responses on the safe side of the unit:- Unit Short-Circuit Open-Circuit 4045B Goes high impedance Goes high impedance 4045C Keeps trying to drive - whatever the load Goes high impedance

• What is the response time of the MTL3073, 4073, 5073, 5074 temperature converter?

  These units convert data every 400ms, i.e. about 2.5 times per second.
  
  The data is pipelined to the output, i.e. the previous sample is output during the time that the current input sample is measured. Hence the maximum delay between a change of input and the output settling may be 800ms. If smoothing and/or damping is selected, then the output will settle to the new value more slowly, but the output update is always 2.5 per second.

• What is WiFi? is it the same as 802.11?

  The Wireless devices that most people refer to as WiFi are in fact devices based on the 802.11 set of standards.  The 802.11 standard was defined by the IEEE in order to allow different vendors to communicate using Radio Waves (though a form of InfraRed communication is also defined in this standard).  The WiFi alliance was set up in order to test various vendors equipment for interoperability, 802.11 is the standard, WiFi proves that it has been tested for interoperability with other vendors equipment.

• What type of information do I need to know when selecting the correct model surge protection device for a signal line?

  The following information would be required:

  1. Operating voltage of the signal line
  2. Maximum load current that will be present on the line
  3. Operating frequency if it is high frequency signal
  4. Number of wires to be protected
  5. Type of connector if a connector is required.
     
• What type of information do I need to know when selecting the correct model surge protection device for a communication/network line?

  You would need to know :

  1. The type of communication line (i.e. RS232, RS485, RS422, CAT 5 Ethernet)
  2. The number of wires to be protected
  3. Type of connector if a connector is required.
     
• What types of communication buses or protocols are applicable for SIL 2 or SIL 3 systems?

  In the process control industries, the simple answer is ‘none’. It is the safety loop that achieves the required integrity level. Communications with a ‘logic solver’ that is performing part of a safety function do not form part of that safety function. The use of HART or other communications may provide diagnostics and confirmation of the state of a safety function but are not themselves part of the safety function.

• What value terminating resistor should I use for RS485?

  The termination will normally be a simple resistive terminator with an impedance that matches the characteristic of the cable; this will normally be in the range 100-220 ohms.
  RS485 interfaces should ideally be provided with a “matched” termination to prevent reflections and “ringing” of the signal on the bus cabling.

• What voltage does the Annunciator operate on?

  Our annunciator range uses 24VDC as a logic voltage.
  
  On P725 annunciators external power supplies are used when the customer has other supply voltages available – typically 120VAC, 240VAC, 125VDC.
  
  On 725B annunciators external or optional internal power supplies are used when the customer has other supply voltages available – typically 120VAC, 240VAC, 125VDC.
  
  As an option Redundant Power Supplies are available

• What's inside the 'Supply Arbitration Modules' of a redundant FISCO system? Are there relays inside?

  Each Supply Arbitration Module (SAM) contains electronic circuits to monitor the output of one FISCO power supply, and to switch the output of that power supply to the field segment. The switching is solid-state, so there are no relays. The two modules communicate with each other by ‘handshaking’ to make sure that they can never both be ‘on’ at the same time.

• Who can conduct a functional safety assessment?

  The steps required to define, design, verify, install and commission safety functions are given in the life cycle contained within the standards. For the process industries the IEC 61511 standard is the sector specific standard to follow and it would be foolish to attempt any activity for a safety function without reference to this standard.

• Who should design safety loop and what competency is required?

  The steps required to define, design, verify, install and commission safety functions are given in the life cycle contained within the standards. For the process industries the IEC 61511 standard is the sector specific standard to follow and it would be foolish to attempt any activity for a safety function without reference to this standard.

• Why are the attached devices not found when using AMS?

  This usually means that the MTL4841 is in the wrong mode. The MTL4841 is available in three different pre-set modes, MTL, AMS and PRM and should be ordered in the required mode to suit your Instrument Manager Software (IMS). If you are unsure which mode your IMS requires, please contact your local MTL representative

• Why are there two Supply Arbitration Modules per fieldbus segment on a redundant FISCO system?

  To eliminates single points of failure for complete redundancy. If one ‘SAM’ fails, the system continues to provide power to the fieldbus segment.

• Why can I see only 49 of the connected HART devices?

  There is a software bug in version 6.0 of the AMS Software that limits visibility to 49 devices. This bug has been fixed in versions above 6.0. Contact your local Emerson office or download the patch from the Emerson website.

• Why do I have problems with Fisher Valvelink and AMS on the same node?

  This problem arises because Fisher Standalone software automatically switches the MTL4841 mode from AMS to MTL when it connects. Unfortunately, when you connect back to AMS, the MTL4841 is in the wrong mode and AMS cannot restore the 4841 to AMS mode. The only advice that can be offered here is don’t use Fisher Valvelink standalone software on the same node as AMS. However, if the Fisher ValveLink software is used as a Snap-On within AMS, this problem will not arise.

• Why do I need to protect data/control lines?

  Data and control interfaces suffer many times more damage from surges than do power supplies. Power supplies normally have some type of filtering and operate at higher voltages than do control or communication interfaces. Low voltage control and communication interfaces normally interface directly into the equipment through a driver or receiver chip. This chip normally has both a logic ground reference as well as the communication reference. Any substantial difference between these two references will damage the chip.

• Why does an AMS reset cause the MTL4841 to reset and lock up?

  You are probably using a very early MTL4841 unit. This condition was corrected at software version 3.4. You should contact your local MTL representative for details on upgrading.

• Why does resetting the IMS confuse the listing of devices?

  This is often because the converter is either not a recommended type or the settings are not correct. MTL recommends using the Westermo MA-45 RS485 converter with the MTL4841.
  Lack of termination and biasing can be another reason for seeing this effect. The RS485 serial line should be terminated and biased and the Westermo converter has internal switches that enable you to do this.

• Why does the MTL4841 scan slowly after a reset?

  The search mode on the MTL4841 has been selected incorrectly. There are three selections, Single Analog, Single Unknown and Multidrop.
  The normal selection is “Single Analog”, this is selected if all of the HART devices have their addresses set to 0.
  “Single Unknown” is used if the poll addresses of the devices are unknown. It will search each loop until it finds a HART device on any poll address, 0-15, as soon as it finds a device it will move to the next loop.
  “Multidrop” is used where there are multiple devices on loops, this will search every poll address, i.e. 0-15, on every loop.

• Why doesn't the IMS show the new HART device I've added?

  When a new device is added, either a “loop rebuild” or a “reset” must be carried out to enable the new device to be seen in the IMS.