Campbell CR800 Series, Руководство оператора

Страница: 369 / 598

Section 8. Operation
369
where
percent-of- reading = 2500 mV • ±0.06%
= ±1.5 mV
and
offset = (1.5 • 667 µV) + 1 µV
= 1.00 mV
Therefore,
accuracy = ±1.5 mV + 1.00 mV
= ±2.5 mV
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.
Figure PGIA with Input Signal Decomposition
(p. 348),
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+ = V
cm
+ V
dm
/2, and V
L
= V
cm
–
V
dm
/2, respectively.
8.1.3 Pulse Measurements — Details
Related Topics:
• Pulse Measurements — Specifications
• Pulse Measurements — Overview
(p. 70)
•
Pulse Measurements — Details
(p. 369)
Read More Review the
PULSE COUNTERS
(p. 369)
and Pulse on C
Terminals sections in
Specifications
(p. 91).
Review pulse measurement
programming in CRBasic Editor Help for the
PulseCount()
and
TimerIO()
instructions.