mpec SA380-IT, Руководство пользователя

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Earth loop resistance out of
tolerance No No Yes
Monitored circuit under voltage Yes No - Affected Circuits
Yes - Unaffected Circuits
Yes
Monitored circuit over voltage Yes No - Affected Circuits
Yes - Unaffected Circuits
Yes
Solid state switch fault No No No
Calibration test failure No No No
2.4) System Voltage Measurement
Voltage is measured across the monitored circuit terminals after the monitored circuit is connected to the measurement circuitry, but prior to
resistance to earth measurement.
If the circuit is configured for measurement, the value of the voltage is calculated. AC RMS
If the circuit is configured for measurement, the value of the voltage is calculated. DC mean
2.5) Resistance to Earth Measurement
Only if the monitored circuits voltage measurement is within tolerable parameters will a resistance to earth measurement be attempted. This
is to ensure safe and reliable operation of the monitored circuit.
The SA380-IT utilises the "pulse test" method of resistance to earth measurement. A series of current limited rectangular pulses are injected
into the monitored circuit. This will cause a current to flow through any resistance and capacitance to earth.
Any capacitance to earth will eventually become fully charged by the test signal. once this occurs, a current measurement can be taken in the
steady state. The combined values of capacitance and resistance to earth will govern measurement time.
2.5.1) AC and DC Circuits
Equivalent Circuit for Measurement Pulse signal
R = Equivalent Resistance to Earth (R in parallel with R ).
L B N
C = System Leakage Capacitance (C in parallel with C ).
E B N
i = Ammeter current solely due to measurement pulse voltage.
Vm
The graph below shows the application of measurement pulses, the transient charging current through the system capacitance and the
A voltage reading of less than 0.5 s regarded as an . times the configured nominal voltage i under-voltage (for example, a reading
Resistance to Earth will not be measured until the under-voltage is removed. of <=25 V on a circuit configured as 50 V).
A voltage reading of more than 1.45 times the configured nominal voltage is regarded as an (for example, a reading over-voltage
of >=72.5 V on a circuit configured as 50 V).
In the above scenarios, r Such an event be caused esistance to Earth will not be measured until the voltage error is removed. could
by hardware failure, but is often simply due to supply voltage variation.