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.

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 per measurement

*** 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 (V2) divided by the voltage measured on the first (V1). If V1 is measured on the 2.5 V range (code 5,15, 25 or 35 in Parameter 2), then the result is 1000 times V2/V1. 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 V1 is the measurement of the voltage drop across the full bridge, and V2 is the measurement of the bridge output. Because the excitation voltage for a full bridge measurement is usually in the

SECTION 9. INPUT/OUTPUT INSTRUCTIONS

2.5V range, the output is usually 1000 V2/V1 or millivolts output per volt excitation.

When used to measure a 4 wire half bridge, the connections are made so that V1 is the voltage drop across the fixed resistor (Rf), and V2 is the drop across the sensor (Rs). As long as V1 is not measured on the 2.5V range, the result is V2/V1 which equals Rs/Rf.

PARAM.

DATA

 

NUMBER

TYPE

DESCRIPTION

01:

2

Repetitions

02:

2

Range code for V1

 

 

(Table 9-1)

03:

2

Range code for V2

04:

2

Differential channel

 

 

number for first

 

 

measurement

05:

2

Excitation channel

 

 

number

06:

4

Excitation voltage

 

 

(millivolts)

07:

4

Input location number

 

 

for first measurement

08:

FP

Multiplier

09:

FP

Offset

Input locations altered: 1 per measurement

*** 10 BATTERY VOLTAGE ***

FUNCTION

This instruction reads the battery voltage and writes it to an input location. The units for battery voltage are volts. When the batteries are around 8 V, false battery readings of 9 to 10 V will result, and the quiescent current drain increases from 0.7 mA to 7 mA. At 9.2 to 9.3 V, false analog measurements are possible (Example: 2000 mV input is measured as 2010 to 2050 mV).

PARAM.

DATA

 

NUMBER

TYPE

DESCRIPTION

01:

4

Input location

Input locations altered: 1

*** 11 107 THERMISTOR PROBE ***

FUNCTION

This Instruction applies a 2 VAC excitation voltage to Campbell Scientific's Model 107

9-5