FAQ - BIM -
FAQ - BIM
| Q |
What Fieldbus protocols are available with MTL Remote I/O ? |
| A | The MTL8000 system has an open architecture which allows it to support a number of different open fieldbus protocols by means of different Bus Interface Modules (BIMs). Modbus : released in November 1997 Profibus-DP : released in October 1998 Ethernet : released in July 2003 |
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| Q |
What is the maximum cable length for the configuration tool? |
| A | The local port of the BIM employs a standard RS232 connection, hence the cable limitation is 15m (50 feet). Note that when using a Modbus BIM it is possible to configure the node remotely via the second LAN highway. Since this is a standard RS485/422 connection the cable length limit will be 1200 metres. |
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| Q |
How are Analog values reported? |
| A | Data values for both Input & Output Analogue variables are handled in the BIM as 16-bit Unsigned Integer values, giving a range of 0 through 65535. This range is applied to an electronic current range of zero through 25 mA. Communication between the Host and the BIM involves raw data within the range/s described. The host then interprets the analog value as engineering units representing the process value/s. |
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| Q |
What is an API? |
| A | An API (Application Programmers Interface) is a piece of software that translates hardware information into a form that can be more easily understood by the user application. It is ‘the filling in a sandwich’. On one side is the user application—user friendly, and user orientated—on the other side is the hardware—often unfriendly and spoken to in engineering terms. An API between these two enables a User to successfully communicate with the hardware. In the case of MTL8000, the API library of commands would be required by any user who wishes to produce a BIM Gateway that interfaces to a non-standard LAN protocol. |
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| Q |
Choice of Node Services Carrier to be used for the Modbus, Profibus-DP, or MOST Controller BIM? |
| A | A choice of carriers are available for mounting the Bus Interface Module (BIM), dependent on the exact system architecture required. The reader is referred to the standard document below, noting the Node Services Carrier numbers : 8711-CA-NS Node Services Module - Modbus 8712-CA-NS Node Services Module - Profibus 8715-CA-BI Universal BIM Carrier 8718-CA-NS Node Services Module - Node Services Module 8750-CA-NS Controller / eBIM Carrier |
| Q |
How does a BIM react to a change in module type, perhaps through a mistake made during maintenance? |
| A | If the type of module inserted in a specific carrier slot location is changed it has to be accompanied by the user changing the configuration data held by the BIM. If the I/O Module is different from the type expected by the BIM’s configuration, the BIM will not allow any data transactions, neither input or output, to occur. The keying system between I/O Modules and Field Terminal Blocks ensure that it is not possible to accidentally replace an I/O Module of one type with a different Module; the user must take positive action to change the Field Terminal Block keying to match an I/O Module type. Once the Field Terminal keys have been adjusted, the new I/O Module may be inserted. Once connected to the Railbus, the BIM will detect that the I/O Module has been replaced and will establish its I/O type, but will not communicate with the new module, if different to the previous device, until configured to do so. |
| Q |
What data rates can we select for Modbus? |
| A | Data rates up to 115.2 kbaud can be selected for the MTL8000 Modbus BIM. When used with redundant LAN communication the maximum data rate is 19.2 kbauds. |
| Q |
How many Modbus nodes can be supported on a single network ? |
| A | Modbus will support up to 247 slaves. However, the RS485 physical layer will only support 32 device loads. The network can be extended above 32 by the use of repeaters. Repeaters may be used to increase the number of deviceson the network, or equally to extend the network length. |
| Q |
Can I have dual Modbus connections ? |
| A | The MTL8000 series is designed for Redundant Modbus LAN connections to each Node. It is possible to connect the two LANs to a host with redundant connections, or to two different hosts. By default the slave address applied to both LANs is identical, but they may be selected, using the Configurator, to independent values. |
| Q |
What data rates can be selected for Profibus-DP ? |
| A | Data rates up to 12 Mbits/s are defined in the Profibus standard, whilst operating speeds up to 6 Mbit/s are supported by the MTL8000 2/x Profibus BIM. The DP network of the MTL8000 1/1 system, being intrinsically safe, has a network data rate limit of 1.5 Mbit/s. The maximum cable length decreases as the data rate increases. The use of stub lines along the network should be avoided where speeds exceed 1.5 Mbits/s. |
| Q |
What is the Hamming Distance in Profibus networks? |
| A | The Hamming Distance is a measure of how secure a protocol is against misinterpretation of a packet with errors as a different legal packet. The ‘packet’ in this context refers to a standard Profibus telegram (data frame). Profibus offers a figure of HD=4, indicating that at least 4 bits have to be wrong, and still match the checksum calculations, in order to be mistaken as another valid packet. This integrity is achieved by a combination of each character in a telegram containing an Even parity check, plus an appended ‘Frame Check Sequence’ character at the end of each Profibus telegram. |
| Q |
Can I locate the BIM in one cabinet and some I/O-modules in a second one? |
| A | The MTL8000 may be used in such a configuration. Extension cables are available as a standard feature of the MTL8000. The restriction is that the total length of such a system layout should not exceed 6.5 metres. |
| Q |
What is the maximum distance from the BIM to the last I/O module using extension cables? |
| A | The maximum distance over which the Railbus can communicate is 6.5m. A maximum of 3 Extension Cables may be used on any one node. Each Extension Cable will require a pair of Carrier Extenders - one for the right-hand end of the ‘feeding’ carrier, the other for the left-hand end of the ‘fed’ carrier. Different cable lengths are available. |
| Q |
Do I lose all data when I swap the BIM? |
| A | A BIM stores its configuration file in Non-Volatile memory (flash EPROM), and hence each time the power is cycled its first subsequent action is to configure all its connected I/O modules into the required state. However, if a new un-configured BIM is introduced, an alternative method of configuring is available using the Node Services Module 8510-MO-NS. This device stores a BIM configuration in non-volatile memory. As the new BIM is installed on the carrier it will automatically upload the configuration from the Node Services Module. This is a very efficient means of replacing the BIM device without pre-configuration. The validity of the configuration data is checked by the BIM before use and if it is found to be corrupt then the BIM would not upload it. |
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