FAQ - isolators -

FAQ - isolators
Q

MTL4041B - What is the input resistance at hazardous area pins 5 and 6?
A Less than 50 ohms, and typically 30 ohms.
  < back
Q

What is the response time for the MTL3073, 4073, 5073, 5074 temperature converters?
A

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.
  < back
Q

What causes the I/P, MTL4045B, DCS output card to 'lock-up'?
A 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.
  < back
Q

MTL4073 - What is the hazardous area input impedance and safe area output resistance?
A 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.
  < back
Q

What is the difference between the MTL4045B and MTL4045C?
A

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
  < back
Q

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

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"
  < back
Q

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

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.
  < back
Q

What distance can I cover between two MTL5051s in separate hazardous areas?
A 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].
  < back
Q

Can I use MTL5000 series for safe area applications?
A 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
  < Back
Q

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

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.

MTL5032 output wiring diagram
  < Back