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Table 4. IDIS Module Current Readings

Circuit Reading Meaning

A1 (Tamper) 1.5mA Tamper loop shorted to 0V.

3mA Open tamper circuit.

3-4mA Potential tamper fault.

4-5mA Voltage drop on 0V line.

5-6mA Good (closed) circuit.

A2 (Alarm) 0mA Open alarm circuit.

3mA Good (closed) circuit.

5.5mA Alarm loop shorted to bus.

A1 & A2 Fluctuating Either data corruption on bus lines, or too much

current being drawn from Programmer. Connect a

12V supply to the Programmer and try again.

Remember to reference to 0V sources where

necessary.

3. For devices other than LIMs try completely disconnecting the device

from its sensor or contacts and looping both the tamper and alarm loops

locally at the module. If that removes the fault then check the wiring of

the tamper/alarm circuits for faults to ground. Check also that the

sensor connected to the module has volt-free contacts and no capaci-

tors fitted across contacts.

If a fault still cannot be fixed by changes to that module or its immediate

wiring then carry on testing using the Thorough Test Method.

Thorough Test Method

1. The IDIS bus may be affected by excessive voltage drop along the 0V

wire. To check the voltage drop (use the same meter for all readings):

a) Check the voltage between 0V an Sig at the Expander Card

(typically 7.8V).

b) Check the voltage between 0V and Sig at the extreme end of each

cable run.

c) If the difference between the two voltages is more than 1.2V then

carry out the suggestions in "Improving the Voltage Drop".

Notes:

a) The voltage reading will vary according to the make/type of meter you use.

b) A Fluke DVM type 83 will read typically 7.8V between 0V and Sig at the

panel.

c) IDIS outputs changing state will change this voltage slightly so do the test

with outputs static.

d) Remember to make sure that anything that can draw current along the 0V

wire is doing so at the time of the measurement.

8136 Thorough Test Method

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