Details; Input Sections; Mux And Adc - Arbiter Systems 928A User Manual

Details

Input Sections

Two identical input channels (A and B) allow users
to connect to voltage sources (0 to 660 Vrms) and to
current sources (0 to 1.2 Arms or 0 to 1.2 Vrms), de-
signed to work with a CT up to approximately 1000
A. To allow accurate measurements at low current lev-
els ( 10 A) there will be a 100 'booster' amplifier
available to extend the input current range downwards
to about 10 – 100 mA (with a 1000:1 external CT) for
full accuracy and lower with somewhat reduced per-
formance. Current Inputs are connected to the upper
connectors and allow for a voltage output or current
output CT. The current input section has a 1000:1 CT
giving an output current of 0 to 1 mA, which is then
converted to a voltage. The voltage input section uses
medium-power, low TC resistors that accept up to 660
Vrms with a 1 Vrms signal to the ADC.
The current input sections are able to accept either
1.2 Arms or 1.2 Vrms max input. This will accommo-
date either current or voltage output probes.

MUX and ADC

The ADC is a 24-bit Texas Instruments ADS1251
sigma delta converter running at 10240 samples-per-
second. There are two multiplexers being used: a
74HC4053 and a 74HC4052. The '4053' is being used
to switch between the voltage and current channel in-
puts, and the '4052' switches the source for current
channels: either a current CT (maximum input 1.2
Arms), voltage CT (maximum input of 1.2 Vrms) or
gain of 20.
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