Problem to read Pulses (Encoder) using 1734-VHSC24 and CompactLogix L19ER-BB1B

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Problem to read Pulses (Encoder) using 1734-VHSC24 and CompactLogix L19ER-BB1B

Post by vinigusto » Sun Jan 05, 2020 11:59 am

Hello guys,

I am running an application for packaging measurement using a sick DFS60B incremental encoder (programmable from 1 to 10000 PPR). In more detail, it passes packaging on a conveyor belt and we have created an inspection station and an expulsion station (defective packaging), so we use the encoder to check at specific points of the packaging for defects (we use special sensors to check defects). ) (there are four in total). However, the problem we are having is the following: When reading the encoder in the PLC, the same means that performs "jumps" and does not enter the windows (GRT and LES) created on the ladder, ie, as if it were not continuous. .

I understand that because the VHSC24 card works at 1 MHz in counter mode, this type of problem should not occur according to our application is not even 100 KHz. For example, our case: Using 1000 PPR and the motor speed (coupling output) is 3600 RPM (in practice it is around 1750 RPM) the frequency is calculated as follows: F = (PPR X RPM) / 60. : F = (1000x3600) / 60 = 60 KHz, ie 60 KHz is much less than 1 MHz, I think this kind of problem does not occur.

Application Info:

. Studio 5000 V31
. PLC Model: Rockwell 1769 - L19ER-BB1B CompactLogix 5370
. Encoder Card: 1734-VHSC24 / C
. Incremental Encoder: Sick, DFS60 up to 10,000 PPR and HTL Electrical Interface. Using a 200 mm circumference / perimeter wheel.
. Motor Nameplate Data: 1670 RPM, 0.37 kW / 0.5 HP, 60 Hz
. Inverter: Weg CFW500, Output Frequency 62 Hz.

Card Settings we use
RPI: 2 ms
Type: Counter, but we already use it as Encoder X1
Store Count Mode: Disabled
Filter: No Filter, but we use 50 KHz and 5 Khz filters in our tests.
Counter Attenuator: 1

Wiring Diagram VHSC24
We turn on encoder A at input 0 and encoder Aret at input 1

In logic
(Structured Text) Using the PMUL instruction to convert encoder (Pulse) data to mm scale.
(Ladder) The window comparisons part (GRT and Les) and other part of the process. We emphasize that we performed the tests also only with the reading and comparison part of the data, excluding the other parts, precisely to verify the issue of Scan, but the problem persisted.

If anyone here in the forum has some information that can help us, I would appreciate it.

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Joined: Wed Nov 18, 2009 4:02 pm

Re: Problem to read Pulses (Encoder) using 1734-VHSC24 and CompactLogix L19ER-BB1B

Post by georg_demmler » Fri Jan 10, 2020 5:15 pm


please check the RPI - 2ms is to fast - check it with 10ms, 20ms and 50ms.


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