Specifications

The Frequency and Timer Input modules feature a versatile input stage that
can be used in a variety of applications. Figure 1 is a block diagram of the
input signal conditioning.
Appendix B
D1600 Data Sheet
Figure B-1. D1601/2 Input Signal Conditioning Block Diagram.
The input signal is applied to a precision comparator through the + input.
Input protection is provided to withstand inputs up to 230Vac. The compara-
tor output is then fed through an opto-isolator to the module’s microproces-
sor for scaling and formatting. The input section is completely isolated from
the power and communications lines. The isolation allows up to 500V of
common-mode voltage between the input ground and the power connec-
tions.
The input comparator employs hysteresis to provide reliable readings with
noisy or slow input signals. The amount of hysteresis may be controlled by
connecting the hysteresis control line (HYSTR) to ground or the 2.5V
terminal through an external resistor. Figure 2 shows the most frequently
used connection.