plc.mitsubishi

FX5 PLC loses impulses from encoder

9 posts in this topic

Hello everyone!
I have strange problem.

I have plc, inverter (mitsubishi), incremental encoder (sick) and motor.
When i set the frequency on the inverter about 1,5Hz, the plc correctly counts impulses, but every higher frequency causes the plc counts impulses incorrectly or doesnt count. 

Above described things are happening at the rotation of motor in the forward direction. With a rotation of the motor to the rear, high-speed counter doesn't count the impulses.

All the parameters of high-speed counters and PLC program i am sure there are right ( i'm using only instruction to start high-speed counting (HIOEN) and to enable interrupt (EI).  Input Response Time i had on "No setting" or 10micro-s and nothing.

Type of encoder - A/B phase, HTL.
PLC - FX5U
PLC program - Gx works 3.

Maybe somebody had similar problem? Maybe somebody could tell me where i need to look for the solve?

 

Thanks for help :)

Share this post


Link to post
Share on other sites

Haven't tested the encoder function on FX5 yet, but did you setup the parameters with an A/B phasae counter so that X0 and X1 (or two others) are defined as A/B counters? Also, you say that the inverter sets to 1,5Hz, but what does that mean for the encoder (how many kHz does that correspond to)?

Since it only counts one way my guess is that you've setup something wrong. Also: I'm pretty sure you shouldn't use both HIOEN and EI at the same time. You setup the high speed function in the parameters.

Share this post


Link to post
Share on other sites

Yes, i setup "2phase 1Multiple". For parameter: High speed counter ch1 i have A for X0, and B for X1. 

Encoder could correspond 10000rpm, at 1,5Hz on the inverter, shaft of encoder rotates with 41,4 rpm.

HIOEN function is required to starts and stops high-speed counting. I deleted EI function but that does not solve the problem.

 

Share this post


Link to post
Share on other sites

I replaced with a new encoder, but that doesn;t solve the problem. So we can rule out mechanical issues.

Share this post


Link to post
Share on other sites

Can you post your program file and give us a part number or specifications on the encoder? A wiring diagram would be helpful too.

Share this post


Link to post
Share on other sites

If It works until a certain frequency make sure that the encoder cable does not travel near the cable that outputs the inverter and goes to the motor. This cable should be shielded but sometimes even if it is shielded at high frequency it can cause disturbances. Try taking the cables out of the raceways and keeping as much distance between them as possible. If it's not an Software issue but an EMC issue like i suspect It will fix your problem.

Share this post


Link to post
Share on other sites

To the OP, you said the input response settings are "no setting" or 10ms. This means you are sampling the encoder at 100hz. But you should be sampling at at least double the maximum frequency of the encoder.

This explains why it's ok at 41.5 rpm but only catches pulses intermittently at higher rpms.

You can lower the input response for the high speed X inputs to 0.6ms minimum giving you around 1.6kHz sampling or 800 pulses per second at the encoder MAX.

If you expect in the application that the encoder can give you over 800pps at higher speeds, you should use a high speed counter card instead.

 

Share this post


Link to post
Share on other sites

If he uses the high-speed input function, he can get up to 200khz sampling (if I remember the specs right). The input response settings are for standard inputs, in other words scanning the inputs and reacting to them in a regular sequence. The high-speed input function allows you to set up at least some of the built-in inputs as high-speed counters or encoder inputs for exactly the purpose the OP is trying to accomplish.

Share this post


Link to post
Share on other sites

Yes sorry, I think JRoss is right. It's different if you're using high speed counting functions. It says the specs are up to 100kHz for 2 phase input.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now