Rockwell Automation T80004 Application Note Field Loop Configuration - Manual (Page 20)

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AN-T80004 Field Loop Configuration
Issue 10 Jun 13 AN-T80004 20
T8424 120V ac Digital Input
The T8424 is actually a T8431 analogue input module with different firmware (and labels). It has to be
used with a T8824 FTA and TC-211, 212, 511 or 512 I/O cables.
The T8824 FTA contains resistor networks that divide the voltage down to analogue input levels. If any
resistor goes open circuit, the overall change in value will not change the input state. In the diagram
below, the field switch is assumed to be volt-free and the field AC input is the 120V ac power supply.
FIELD AC
INPUT
(0 - 150Vrms)
FIELD
SWITCH
(4 x 4) 68K
(4 x 4) 1K
(0 - 2.2Vrms)
AC Out to
T8424 Module
50mA Fuse
The T8424 does not recognize a threshold template; if one is downloaded it will be ignored. It has fixed
state change (hysteresis) voltages. Voltages below 26V ac are reported as ‘off’ (state 2) and voltages
above 82V ac are reported as ‘on’ (state 4) with the last reported state held between these voltages.
The module can measure up to 150V ac.
States
Input Voltage
(RMS) 82V+/-10% 26V+/-10%
2
4