User's Manual

Table Of Contents
7ML19985JE03 SITRANS LR250 (HART) INSTRUCTION MANUAL Page 27
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Wiring
Passive Shunt Diode Barriers
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 any additional series
resistance, for example, PLC inputs and/or displays)
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.
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.
Use the values for Vworking and Rworking to confirm that operation is within the
shaded area of the graph
Curve 1 (General Purpose, Intrinsically Safe, Non-incen-
dive)
on page 140.
Active barriers (repeating barriers)
Note: A well regulated supply voltage is required.
Manufacturer Part Number
MTL 787SP+ (Dual Channel)
MTL 7787P+ (Dual Channel)
Stahl 9001/01-280-100-10 (Single Channel)
Stahl 9002/01-280-110-10 (Dual Channel)
Manufacturer Part Number
MTL 706
MTL 7206
Siemens SITRANS I 7NG4122
Stahl 9001/51-280-110-14
MTL E02009
MTL E02010