Campbell Scientific AM16/32A Multiplexer - Manual (Page 25)

AM16/32A Relay Analog Multiplexer
GENERALIZED CRBASIC PROGRAMMING SEQUENCE:
ACTIVATE MULTIPLEXER/RESET INDEX
Portset (1 ,1) 'Set C1 high to Enable Multiplexer
I=0
BEGIN MEASUREMENT LOOP
SubScan(0,sec,16)
CLOCK PULSE AND DELAY
Portset
(2,1 ) ‘Set port 2 high
Delay (0,20,mSec)
Portset (2,0) ‘Set port 2 low
INCREMENT INDEX AND MEASURE
I=I+1
'User specified measurement instruction
‘Storing results in Variable(I)
END MEASUREMENT LOOP
NextSubScan
DEACTIVATE MULTIPLEXER
Portset (1 ,0) 'Set C1 Low to disable Multiplexer
In addition to precision voltage excitation, the CR5000 and CR3000
have programmable current excitation. Current excitation allows a
resistance measurement on a four-wire sensor (e.g., a PRT) such as
shown in Figure 14 using only a single differential channel and no
fixed resistor; the excitation return goes directly to ground. With the
current excitation the resistance of the relays and lead wire do not
affect the measurement.
5.3.1 CR5000 and CR3000 Programming
Although the following example is a CR5000 program, a similar
program can be used for the CR3000. This CR5000 program uses the
AM16/32A to measure 16 100 ohm Platinum Resistance
Thermometers connected in the 4x16 configuration. The program
also measures 6 copper constantan thermocouples.
CR5000 AM16/32A PRT(4 Wires)
Control/Common Sensor Terminals
C1 Reset Odd H Excitation
C2 Clock Odd L Excitation Return
IX1 COM Odd H Even H Sense wire excitation side
IXR COM Odd L Even L Sense wire return side
7H COM Even H
7L COM Even L
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