Pakscan IIE System Manual
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Publication S177E V2.0 Issue 03/05
Make sure that no two field units on the loop have the same address, and that no field unit has an
address set higher than that selected as 'the highest address' - see section 9.3.
When setting and checking a field unit remember that the Paktester will only communicate to one field
unit at a time, the one to which it is connected. Also remember that the address and baud rate can
only be altered if the field unit is in loopback.
13.2 Checking the Loop Itself
The most common problem in commissioning is that the field wiring is incorrectly made. If the cable is
not connected correctly between the Output side of one field unit and the Input side of the next then
the loop will fail to operate. As powered ‘off’ field units divert the signal directly from input to output a
simple resistance check will not reveal this cabling error. Similarly if the cable is 'twisted' so that the
common wire is not connected to all the common terminals this will also not be revealed by a simple
resistance check.
It is extremely important to check all the wiring to ensure it is correctly connected throughout the loop.
Checking the Loop with the Master Station
Initially set the Loop Driver circuits to deliver maximum loop voltage. Do this by turning the two
potentiometers fully anti-clockwise.
Connect Port A wiring only to the master station and leave Port B disconnected. This time make sure
that all the field units except the one furthest away are powered off. Select the Master Station Status
screen, go to the Master Station Commands screen, and Reset the Loop by pressing '1'. Return to the
Status screen (by pressing 'Menu').
Hint:
The loop wiring can often be checked by using a Paktester attached to one the end of the cable,
then power ‘on’ all the actuators and successively power them ‘off’ starting with the one nearest
the master station. The Paktester manual (S178E) has an illustration showing how to connect the
Paktester.
This is only possible if the total loop resistance is
less than 200 ohms
.
Disconnect the loop wiring from the master station; connect the Paktester to the wires that were
connected to Port A of the master station. Ensure that all the actuators are switched on. The
Paktester should be able to establish communication with the nearest field unit to the master
station. Once communication is verified, switch off the nearest field unit, and repeat the
communication test with the next field unit. Successively power ‘off’ each field unit ‘forwards’ round
the loop until communication has been verified with all the field units. Make a note of the order of
the addresses of the field units on the loop (i.e. a Map).
Establishing communication in this way verifies the loop cabling, except for the final connection
from the last field unit back to Port B of the master station. To check this final part of the wiring
connect the Paktester to Port B wires (ensuring the correct polarity) and establish that you can
communicate with the field unit nearest Port B.
