IMC C SERIES User Manual page 70

70 Device description
5.1.1.3.7.1 Connection: Open-Collector Sensor
Simple rotary encoder sensors are often designed as an Open-Collector stage which outputs a signal
which ranges between the states 0 V and SUPPLY. In this case, the switching threshold should be set to
half the SUPPLY voltage:
sensor
5.1.1.3.7.2 Connection: Sensors with RS422 differential line drivers
Commercially available rotary encoders are often equipped with differential line drivers, for instance as
per the EIA-standard RS422. These deliver a complementary (inverse) TTL-level signal for each track. The
sensor's data are evaluated differentially between the complementary outputs. The threshold to select is
0 V, since the differential evaluation results in a bipolar zero-symmetric signal: 3.8 V to 5 V (HIGH) or –
3.8 V to 5 V (LOW). Ground loops as pure common mode interference are suppressed to the greatest
possible extent.
The illustration below shows the circuiting. The reflection response and thus the signal quality can be
further improved by using terminator resistors.
sensor
(SUPPLY)
Ua
RS422
-Ua
POWER_GND
© 2018 imc Test & Measurement GmbH
cable
(SUPPLY)
Ua
SIGNAL_GND
POWER_GND
sensor with open-collector output
cable
sensor with RS422 differential output
ENC-4
+5V
+INA
+/-30V
-INA
GND
CHASSIS
ENC-4
+5V
+INA
a
R_
ter
+/-30V
m
-INA
GND
CHASSIS
imc C-SERIES - Manual, Version 4 R 3 - 2018-10-19