PLC5 Analog Output acting funky?

Hey guys,

I have a problem that is puzzling me on a PLC 5 system. I am using a 4-20mA analog output (1771-OFE2/B) straight to a Powerflex 4m drive to run a small motor. This has supposedly worked before, but for some reason, all of a sudden we have no control over the motor. It just runs at a set speed.

Now, normally I would think that drive parameters were changed, to make it run off a preset speed, but that has been checked. The drive is definitely set for a 4-20mA input source signal. We have a pot, that is wired into the PLC, which gives us a speed setting(where the operator wants to run at). We manipulate it in the program for various reasons, and output this manipulated signal to the drive in the form of a 4-20mA signal. However, if we put a meter in series with the output, all we see is a never changing 12mA. And the drive runs at half its max speed, which I would expect it to do. However that is not what we are telling it to do. As we turn the pot, we see the value being written out to the analog card changing, we are just not seeing it physically change on the meter.

The BTR/BTW doing this, is in Ladder 4, on rungs 11 and 12. Whenever I click on the setup for these instructions, it displays a message saying something to the effect of "setup is not available/not configured". The values (2047) that the BTR is retrieving, do appear to be correct(half of 4095 being 12mA). It just doesn't seem to be writing out TO the card what we actually want the value to be.

Also, and this may be completely normal, if we put a scope on the output of the analog card, it doesnt display a smooth DC signal. It is more like a pulsating DC. We tried changing the analog card to no avail.

I have attached a zipped copy of the program in RSP format. Any help would be appreciated in explaining what is going on here!
Thanks

Have you just put a current meter on the output card to measure the mA signal directly?

Also, is this a new or existing card? Are you writing the configuration to the card properly? If I recall you have to use a BTW to write things like the range, current/voltage to the card (Forgive me been a few years since I worked on a PLC5 system).

Well we tried using 3 different Flukes to measure the mA going to the drive, they all registered like 0.1, 0.2mA. No blown fuses, hooked up in series with the leads in the correct holes. We then put an analog meter on there, and that is what is showing us the 12mA. And the drive does indeed seem to be running at half speed. Max speed is set to 110Hz, and it is running about 57Hz. If I lower the Max Speed to say 60Hz, the actual speed goes to 30Hz, exactly half.

In terms of setting up the card properly, thats a grey area for me. Like I said in my first post, normally there is a setup screen where you can edit things like the range and what not. But in this case, it says there is no setup screen available. Not sure if that is right or not. I have other machines in the plant where I have seen the same message but am not having trouble with those machines (or haven't noticed any way).

PLC5's do not require the I/O to be configured. But if you add the card manually the cards configuration will show up. I have taken the liberty to do so. See picture below.

The channels are controlled by registers N34:145 thru N34:148, those registers are written to by N27:91 thru N27:94. I don't see anything writing to channel 1 N27:92 ( it has a value of -4 now). I don't think this is your problem but you might try manually writing to register N27:92 ( something positive between 0-4095)

Do the other chanenls work? You may have a bad channel.

Thanks Mickey, that is the screen I can't get to. How did you open that up? Do you have to be offline perhaps? I don't have RSlogix with me at the moment to try.

We are only using 1 channel on this card, and have not tried any of the others, however we did try a whole brand new card.

You have to add the card to the I/O configuration manually, because you already had the BTR/BTW instruction configured the software will show you how its setup after you add the card.

Edit: I see rereading your first post the Register gets written to by an operator interface.

I would still try writing to it manually. ( N27:92)

Interesting, you have answered a question I have had for a long time. Thank you.

Tomorrow i will go ahead and add the card to make sure I remember how in future. And will also write to N27:92 to see how it responds.

The BTR/BTW shows the module in rack 1 group 5. The remote I/O channel configuration shows racks 2,3,5,6,7. Is this module installed in the resident rack with the processor?

A 16 slot chassis? Or??

Which channel are you using? Channel 1 ( second channel) shows a value of 2047 which is controlled by N27:92.
Channel 0 ( first channel) is controlled by N27:91.