7Tutorial
288 Keysight 34970A/34972A User’s Guide
Calculation Error
An error is inherent in the way a thermocouple voltage is converted to a
temperature. These calculation errors are typically very small compared to the
errors of the thermocouple, wiring connections, and reference junction (see page
278).
DC Voltage Measurements
To make a useful DC meter, a “front-end” is required to condition the input before
the analog-to-digital conversion. Signal conditioning increases the input
resistance, amplifies small signals, and attenuates large signals to produce a
selection of measuring ranges.
Signal Conditioning for DC Measurements
Input signal conditioning for DC voltage measurements includes both
amplification and attenuation. A simplified input to the internal DMM is shown
below.
For input voltages less than 12 VDC, the Low V switch is closed and applies the
input signal directly to the input amplifier. For higher voltages, the High V switch
is closed and the signal is attenuated 100:1 before being applied to the input
amplifier. The input amplifier gain is set to one of three values (x1, x10, or x100) to
yield a signal in the range of ±12 VDC for the analog-to-digital converter.
HI
LO
Low V
High V
100:1
X1
X10
X100
Ranging
+/- 12 Vcd to
Analog-to-Digital
Converter
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