Rockwell Automation 1756-CFM ControlLogix Configurable Flowmeter Module - Manual (Page 138)

138 Rockwell Automation Publication 1756-UM010B-EN-P - December 2011
138 Schematics
Gate Inputs
Gate inputs are used for running prover and store count values. There is one
gate associated with each flowmeter input circuit (G0 corresponds to F0).
To turn on a gate circuit, you must source current through the input resistors
sufficient to turn on the opto-isolator in the circuit. If no connection is made
to the pair of gate terminals, no current will flow through the photodiode of
the opto-isolator and that gate will be OFF (the corresponding input status
indicator is OFF).
The input current magnitude can be determined by:
Z0 RET
Z1 RET
physical and electrical isolation
Z0 (5V)
Z1 (5V)
2
1
Input
6
5
RET
1k
R2
150
R1
D1
D3
D2
Q1
R6 R7
C28
+5V
U2
C26
42846
4
3
Z0 (12-24V)
Z1 (12-24V)
C27
Z0
Z1
CASE A – for 5V DC operation CASE B – for 10 to 31.2 V DC operation
gate input current = (gate input voltage - 2V 1 )
150 (See note 2)
Examples
1. If gate input voltage = 5V DC
gate input current =(5V-2V)
150
gate input current = 20mA
gate input current = (gate input voltage - 2V 1 )
1150 2
Examples
1. If gate input voltage = 10V DC
gate input current =(10V-2V)
1150 (See note 2)
gate input current = 7mA
Examples
1. If gate input voltage = 5V DC
gate input current =(31.2V-2V)
1150 (See note 2)
gate input current = 25.4mA
1 . There is approximately a 2V drop across (Q1 + the photodiode).
2 . The operating range of the input is 5-10mA and Q1 functions as an overcurrent protection circuit. If an open collector
device with pull-up is used, the value of the pull-up must be added to the  value shown in the denominator.