Rockwell Automation T8403 Trusted 24V dc Digital input Module - 40 Channel - Manual (Page 11)

Trusted
TM
Module T8403
Issue 15 Jun 13 PD-T8403 11
1.5. Line Monitoring Thresholds
The module determines the contact state and line fault status by comparing the input voltage level to
four user programmed thresholds and two fixed (minimum and maximum) thresholds. A “Contact
Indeterminate” region is defined between the contact Closed and Open states to account for marginal
faults in the external wiring or in the IFIU. Hysteresis is provided on the thresholds by up-scale and
downscale values, corresponding to the thresholds for increasing and decreasing values respectively.
Typical
voltage
threshold
values
Input
Channel
State
DI
Status
Line
Fault
Status
Over-range 7 0 1
Tmax 36.00
Short Circuit 5
T8 22.00
4 or 51 0/1 0/1
T7 21.00
Contact Closed 4 ‘1’ 0
T6 12.75
3 or 4 0/1 0/1
T5 12.25
Contact Indeterminate 3 0 1
T4 11.75
2 or 3 0
T3 11.25
Contact Open 2
T2 3.00
1 or 2 0/1
T1 2.00
Open Circuit 1 1
Tmin -8.00
Under-range 7
Table 1 Example Threshold data
When a module is inserted into the standby slot in a line-monitored application, then the field
terminations for all the input channels are paralleled, resulting in a drop in the input voltages for the
active module. Therefore the recommended components for line monitoring are zener diodes, one in
parallel with the field switch which is across the supply and signal, the other in series with the signal.
1 The channel state value returned is dependent on the previous state value. If the input level is
increasing then the lower state value will be returned. If the input level is decreasing the higher state
value will be returned.