Rockwell-automation 1734-IK Encoder/Counter Modules User Manual Manuel d'utilisateur télécharger pdf (Page 9)

Publication 1734-UM006B-EN-P - August 2005

Preface 3

Definitions

The following define the intended operation of the Encoder/Counter

module.

Term Definition

Lead Breakage Typically requires a shunt resistor (across the load) to detect

3 levels of current/input states -

• Open (Wire Off, Device = ?)

• Off (Wire OK, Device Off)

• On (Wire OK, Device On)

This method does not check the input against a time base,

only that the device wiring (current loop) is intact

Missing Pulse Typically uses an input pulse to reset a watchdog timer (fixed

or programmable HW). This method does detect “Lead

Breakage”, since a broken wire will time-out the watchdog.

Zero Frequency Typically uses an input pulse to calculate an input frequency

and verify it is above an error threshold. This method does

detect Lead Breakage, since a broken wire will generate a

0Hz frequency.

Missing Pulse or Zero Frequency will also detect a customer

device stuck high or low, since the counter is monitoring for a

change in the input state. Currently, the Counter/Encoder

Modes do not have Zero Frequency Detection - the A & B

inputs are time independent, only looking for input edge

changes to increment/decrement the count value.

The Period/Rate and Continuous Rate modes do have Zero

Frequency Detection, since the Z input is monitored for Zero

Frequency in Firmware (A and B inputs are not used and not

monitored).

The Rate Measurement mode inherently has Zero Frequency

Detection, since no A pulses in any sample period are = 0Hz

(B and Z inputs are not used and not monitored).

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Rockwell-automation 1734-IK Encoder/Counter Modules User Manual Manuel d'utilisateur Page 9