Startco Engineering Ltd. Page 37
FPU-16 Feeder Protection Unit Rev. 0
Pub. FPU-16-M, November, 1997 Downloaded from the Internet, see Disclaimer.
5.5 ANALOG MODULE
The analog module contains input circuits for phase current, operation counter,
and earth-leakage current. It also contains an eight-channel, multiplexed, ten-
bit, A/D converter and an isolated analog-output circuit. All inputs and outputs
have MOV protection against electrical transients.
Serial data are transferred to the isolated analog-output circuit through a dual-
channel optical isolator. The analog signal is scaled and buffered to provide the
required current or voltage output.
5.6 OPTION MODULES
A 50-pin bus connector on the display module accepts a backlighting, remote
input, or RS-485 communications interface module.
5.7 FIRMWARE
The FPU-16 has a two-cycle sampling interval followed by a one-cycle
calculation interval.
In each sampling interval, the multiplexed A/D converter obtains 200 samples of
the earth-fault and phase-current signals. The multiplexer sequences these four
signals so that each measurement is a digital integration of 50 samples
uniformly spaced throughout the sampling interval.
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