Rockwell Automation 1734-IK Encoder/Counter Modules User Manual - Manual (Page 36)

Publication 1734-UM006B-EN-P - August 2005
3-4 Input and Output Data
Zero frequency Detected (ZD) - This bit is operational when
frequency configurations are programmed (configurations: period/rate
[5], rate measurement [7]).
In period/rate [5] configuration, counts are acquired during
the ON state of the Z input. At very low frequencies the counter
saturates, indicating a zero frequency detect. The time it takes to
determine a zero frequency in these two configurations can be
as long as 6.7 seconds ( 16,777,216 counts x 1/5MHz x 2 half
cycles of Z ).
In rate measurement [7] configuration pulses on the A input
are counted over a sample interval specified by the time base.
The time it takes to determine a zero frequency in this
configuration will be determined by the sample interval, for
example, time base = 0.300 second (300 milliseconds) to
determine ZF.
Configuration Data The following represents the configuration data used by the module.
Parameter Configuration Information Size (bytes)
1 Set/Get Counter Configuration 1
2 Set/Get Filter Selection 1
3 Set/Get Decimal Position 1
4 Set/Get Reserved 1
5 Set/Get Time Base 2
6 Set/Get Gate Interval 1
7 Set/Get Scalar 1
8 Set/Get Rollover Value 4
9 Set/Get Preset Value 4
10 Set/Get Counter Control SS Value 1