Campbell Scientific CR510 Basic Datalogger - Manual (Page 109)

SECTION 9. INPUT/OUTPUT INSTRUCTIONS
9-5
resulting value, which is the ratio of the voltage
across the sensor to the voltage across the
reference resistor. A 1 before the excitation
channel number (1X) causes the channel to be
incremented with each repetition.
PARAM. DATA
NUMBER TYPE DESCRIPTION
01: 2 Repetitions
02: 2 Range code for both
measurements (Table
9-1)
03: 2 Single-ended channel
number for first
measurement
04: 2 Excitation channel
05: 4 Excitation voltage
(millivolts)
06: 4 Input location number
for first measurement
07: FP Multiplier
08: FP Offset
Input locations altered: 1
*** 8 DIFFERENTIAL VOLTAGE WITH ***
EXCITATION AND DELAY
FUNCTION
This measurement consists of applying a single
excitation voltage, delaying a specified time,
and making a differential voltage measurement.
The result stored is the voltage measured.
"Delay" (Parameter 5) refers to increasing the
signal settling time by increasing the time
between the start of excitation and the start of
signal integration (Section 13.2). If a delay of 0
is specified, the inputs for the differential
measurement are not switched for a second
integration as is normally the case. With the 0
delay, Instruction 8 does not have as good
resolution or common mode rejection as other
differential measurements. It does provide a
very rapid means of making bridge
measurements. This instruction does not
reverse excitation. A 1 before the excitation
channel number (1X) causes the channel to be
incremented with each repetition.
The 50 and 60 Hz rejection ranges (Section
13.1) do not have enough time between
integrations to allow a delay.
PARAM. DATA
NUMBER TYPE DESCRIPTION
01: 2 Repetitions
02: 2 Range code (Table 9-1)
03: 2 Differential channel
number for first
measurement
04: 2 Excitation channel number
05: 4 Delay (0.01s)
06: 4 Excitation voltage
(millivolts)
07: 4 Input location number
for first measurement
08: FP Multiplier
09: FP Offset
Input locations altered: 1
*** 9 FULL BRIDGE WITH EXCITATION ***
COMPENSATION
FUNCTION
This instruction is used to apply an excitation
voltage and make two differential voltage
measurements. The measurements are made
with both positive and negative excitation
voltage. The measurements are made on
sequential channels. The result is the voltage
measured on the second channel (V
2
) divided
by the voltage measured on the first (V
1
). If V
1
is measured on the 2.5 V range (code 5,15, 25
or 35 in Parameter 2), then the result is 1000
times V
2
/V
1
. A 1 before the excitation channel
number (1X) causes the channel to be
incremented with each repetition.
When used as a 6 wire full bridge (Figure 13.5-
1), the connections are made so that V
1
is the
measurement of the voltage drop across the full
bridge, and V
2
is the measurement of the bridge
output. Because the excitation voltage for a full
bridge measurement is usually in the 2.5 V
range, the output is usually 1000 V
2
/V
1
or
millivolts output per volt excitation.
When used to measure a 4 wire half bridge, the
connections are made so that V
1
is the voltage
drop across the fixed resistor (R
f
), and V
2
is the
drop across the sensor (R
s
). As long as V
1
is
not measured on the 2.5V range, the result is
V
2
/V
1
which equals R
s
/R
f
.