13-4
Testing and Troubleshooting
Date Code 20011205
SEL-311B Instruction Manual
Low-Level Test Interface
The SEL-311B Relay has a low-level test interface between the calibrated input module and the
separately calibrated processing module. You may test the relay in either of two ways: by using
secondary injection testing or by applying low magnitude ac voltage signals to the low-level test
interface. Access the test interface by removing the relay front panel.
Figure 13.1 shows the low-level interface connections. This drawing also appears on the inside
of the relay front panel. Remove the ribbon cable between the two modules to access the outputs
of the input module and the inputs to the processing module (relay main board).
You can test the relay processing module using signals from the SEL-RTS Low-Level Relay Test
System. Never apply voltage signals greater than 9 volts peak-peak to the low-level test
interface. Figure 13.1 shows the signal scaling factors.
CAUTION
!
The relay contains devices sensitive to Electrostatic Discharge (ESD).
When working on the relay with front or top cover removed, work
surfaces and personnel must be properly grounded or equipment
damage may result.
You can test the input module two different ways:
1. Measure the outputs from the input module with an accurate voltmeter (measure signal
pin to GND pin), and compare the readings to accurate instruments in the relay input
circuits, or
2. Replace the ribbon cable, press the front-panel
<METER>
button, and compare the relay
readings to other accurate instruments in the relay input circuits.
Figure 13.1: Low-Level Test Interface
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