Rockwell Automation 8520 9/Series CNC Integration Maintenance Manual Documentation Set - Manual (Page 118)

Section 3A
Primary 9/230 Components
3A-35
Figure 3A.24
Internal Circuitry Supporting the Touch Probe
5V
common
+ 5V dc
464ohm
1000ohm
4 3 2 1
19534
75ALS197
dc
TB2
The following table indicates probing threshold voltages. Maximum Input
Threshold (critical if the control has been configured to fire on the falling
edge of the probe signal) indicates the voltage that the probe signal must
fall below to be considered as “fired”. Minimum Input Threshold (critical
if the control has been configured to fire on the rising edge of the probe
signal) indicates the voltage that the probe signal must rise above to be
considered as fired
Probe Thresholds Voltage at Threshold
Minimum Input Threshold (probe circuit) 2.875 (min)
Maximum Input Threshold (probe circuit) 2.125V dc (max)
To avoid misfires use the threshold values from the above table to
determine the necessary signal voltage for steady state operation (probe not
fired). For probes configured to fire on the falling edge the steady state
voltage must remain above 2.875 volts. For probes configured to fire on
the rising edge the steady state voltage must remain below 2.125 volts.