Campbell CR1000X - Minimizing Electronic Noise

Minimizing electronic noise
Electronic noise can cause significant error in a voltage measurement, especially when measuring
voltages less than 200 mV. So long as input limitations are observed, the PGIA ignores voltages,
including noise, that are common to each side of a differential-input pair. This is the common-
mode voltage. Ignoring (rejecting or canceling) the common-mode voltage is an essential
feature of the differential input configuration that improves voltage measurements. The
following image illustrates the common-mode component (V
cm
) and the differential-mode
component (V
dm
) of a voltage signal. V
cm
is the average of the voltages on the V+ and V–
inputs. So, V
cm
= (V+ + V–)/2 or the voltage remaining on the inputs when V
dm
= 0. The total
voltage on the V+ and V– inputs is given as V
H
= V
cm
+ V
dm
/2, and V
L
= V
cm
– V
dm
/2,
respectively.
6. Measurements 52