7ML19985QX81 SITRANS LR250 (HART) – QUICK START MANUAL Page EN-9
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English
How to select a passive barrier for SITRANS LR250
To make sure that the barrier safety description is suitable for the LR250 Intrinsically Safe (IS)
input parameters, carry out the following calculations:
Re-e = max. end-to-end resistance of the barrier
Rloop = loop resistance (total of cable resistance plus e.g. sense resistance,
displays, and/or PLC inputs)
Vbarrier = value of any non-linear voltage drops due to the barrier
1. Determine the value for Re-e from the data sheet.
2. Calculate the total value for Rloop: by adding, for example, sense resistance, displays,
and/or PLC inputs.
3. Calculate Rworking = Re-e + Rloop.
4. Determine the value of Vbarrier from the barrier data sheet (for example, voltage drops
due to diodes).
5. Calculate Vworking = Vsupply – Vbarrier.
6. Use the values for Vworking and Rworking to confirm that operation is within the shaded
area of the graph
Loop Voltage versus Loop Resistance
on page 21.
Active barriers (repeating barriers)
Stahl 9001/01-280-100-10 (Single Channel)
Stahl 9002/01-280-110-10 (Dual Channel)
Manufacturer Part Number
MTL 706
MTL 7206
Stahl 9001/51-280-110-14
Pepperl+Fuchs KSD2-CI-S-Ex
Pepperl+Fuchs KFD2-STC3-Ex1
MTL E02009 - verify
MTL E02010
Manufacturer Part Number (continued)
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