Operator`s manual

SECTION 13. 21X MEASUREMENTS
13-17
FIGURE 13.5-2. Excitation and Measurement
Sequence for 4 Wire Full Bridge
TABLE 13.5-1. Comparison of Bridge
Measurement Instructions
Instr. Circuit Description
4 DC Half Bridge User entered settling
time allows
compensation for
capacitance in long lead
lengths. No polarity
reversal. One single-
ended measurement.
Measured voltage
output.
5 AC Half Bridge Rapid reversal of
excitation polarity for ion
depolarization. One
single-ended
measurement at each
excitation polarity.
Ratiometric output.
6 4 Wire Slightly lower noise than
Full Bridge 9. One differential
measurement at each
excitation polarity.
Ratiometric output.
7 3 Wire Compensates for lead
Half Bridge wire resistance,
assuming resistance is
same in both wires.
Two single-ended
measurements at each
excitation polarity.
Ratiometric output.
8 Differential Makes a differential
Measurement measurement without
with Excitation reversing excitation
polarity or switching
inputs. Used for fast
measurements on load
cells, PRTs etc.
Resolution and common
mode rejection worse
than 6 if used with
delay=0. Measured
voltage output.
9 6 Wire Compensates for lead
Full Bridge wire resistance. Two
or 4 Wire differential
Half Bridge measurements at each
excitation polarity.
Ratiometric output.
Calculating the actual resistance of a sensor
which is one of the legs of a resistive bridge
usually requires the use of one or two
Processing Instructions in addition to the bridge
measurement instruction. Instruction 59 takes
a value, X, in a specified input location and
computes the value MX/(1-X), where M is the
multiplier and stores the result in the original
location. Instruction 42 computes the reciprocal
of a value in an input location. Table 13.5-2
lists the instructions used to compute the
resistance of any single resistor shown in the
diagrams in Figure 13.5-1, provided the values
of the other resistors in the bridge circuit are
known.