GE L90 Instruction Manual page 115

CHAPTER 3: INSTALLATION
alarms. For customers using firmware revisions below 5.60, it is not required to match the revision of the modules installed.
The UR-series C37.94SM communication module has six switches that are used to set the clock configuration. The
following figure shows the functions of these control switches.
For the internal timing mode, the system clock is generated internally. Therefore, set the timing switch selection to internal
timing for relay 1 and loop timed for relay 2. There must be only one timing source configured.
For the looped timing mode, the system clock is derived from the received line signal. Therefore, set the timing selection to
loop timing mode for connections to higher-order systems.
The C37.94SM communications module cover removal procedure is as follows:
1. With power to the relay off, remove the C37.94SM module (module 2A or 2B) as follows. Record the original location of
the module to help ensure that the same or replacement module is inserted into the correct slot.
2. Simultaneously pull the ejector/inserter clips located at the top and at the bottom of each module in order to release
the module for removal.
3. Remove the module cover screw.
4. Remove the top cover by sliding it towards the rear and then lift it upwards.
5. Set the timing selection switches (channels 1 and 2) to the required timing modes (see description earlier).
6. Replace the top cover and the cover screw.
7. Re-insert the C37.94SM module. Take care to ensure that the correct module type is inserted into the correct slot
position. The ejector/inserter clips located at the top and at the bottom of each module must be in the disengaged
position as the module is inserted smoothly into the slot. Once the clips have cleared the raised edge of the chassis,
engage the clips simultaneously. When the clips have locked into position, the module is inserted fully.
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
Figure 3-52: Switches
PILOT CHANNEL COMMUNICATIONS
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