Schweitzer Engineering Laboratories SEL-352-1 - Channel Offset; Master Offset; Power Supply; Temperature

Date Code 20010731 Metering and Monitoring 6-9
SEL-352-1, -2 Instruction Manual
All failures, represented by an F in the status report, generate an automatic serial port message,
display the failure on the front-panel display, and latch the ALARM output contact.
Channel Offset
The relay measures the dc offset (OS) voltage of each analog input channel and compares the
value against a fixed limit of 30 mV. If an offset measurement is outside the fixed limit, the
relay declares a warning.
Master Offset
The master offset (MOF) test checks the dc offset in the multiplexer/analog to digital converter
circuit. The relay selects a grounded input to sample for dc offset. If the offset measurement
exceeds 20 mV, the relay declares a warning. If the offset measurement exceeds 30 mV, the
relay declares a failure.
Power Supply
The relay measures the internal power supply (PS) voltages and regulated +5 and –5 voltages
and compares the values against fixed limits. If a voltage measurement is outside the limits, the
relay declares a warning or failure. See Section 3: Breaker Logic for the limits.
Temperature
The relay measures internal temperatures (TEMP) within itself. If the relay measures a
temperature less than –40C or greater than 85C, the relay declares a warning. If the relay
measures a temperature less than –50C or greater than 100C, the relay declares a failure. The
temperature warning does not pulse the ALARM output contact.
RAM
The relay checks the random-access memory (RAM). If the relay can neither write to nor read
from a byte, the relay declares a RAM failure. There is no warning state for this test.
Flash ROM
The relay computes a checksum to check the flash read-only memory (ROM). If the computed
value does not agree with a stored value, the relay declares a ROM failure. There is no warning
state for this test.
Analog-to-Digital Converter
The relay checks the A/D conversion time to verify A/D converter function. The test fails if
conversion time is excessive or a conversion starts and never finishes. There is no warning state
for this test.