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Unread November 19th, 2019, 02:30 PM   #1
Ken Moore
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How fast can a PLC-5 Analog output "run"

Old equipment, trying to run faster than designed.
I have a client that is still running a PLC5/40 on an extruder line. They are using a 10ms STI to read encoder values BTR and send speed to a drive via a BTW to a local AO card ( not remote IO). The drive powers a "puller" that runs about 10% above the extruder speed. So as the extruder ram changes speeds, the puller has to match.


They have slowly over the years increased line speed by about 50%. Now randomly, a new Siemens S120 drive will fault with "encoder" fault. I suspect the old resolver encoder they have on the motor is the issue, but just wanted to brain storm a bit.
The folks who installed the new drive say it's a plc problem, but supposedly all the problems started with the new drive. No proof of this.

If they slow down the line by about 10%, almost no issues.

Just for my own knowledge, does anyone know how fast a 1771-OFE1 and 1771-IFE can process at?
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Unread November 19th, 2019, 02:49 PM   #2
JRW
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Ken

I don't see how your AB analog would trigger an "encoder" fault
Can you get more details?
So this is an old motor with a resolver?
I could ask a million questions but a real fault number from the drive goes a long way

Have them run the drive from Starter software (using Starter control panel, speed it up and down) - this will eliminate your analog in- then see if the drive still faults

Last edited by JRW; November 19th, 2019 at 02:59 PM.
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Unread November 19th, 2019, 03:12 PM   #3
Ken Moore
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Yes it's about 20 year old motor and resolver, not sure of exact drive fault. Does not have a display on it. Operators have gotten used to it, fault reset, recover, run some more.

Per the maintenance guy, the drive faulted a lot when installed, and the "drive guys" said it was always an encoder fault, then said the PLC had to be "fixed".
I am here to fix the PLC, old PLC-5 support is becoming hard to obtain. None of our new guys know it, or want to learn, can't blame them.

My boss said the drive issues are out of our scope, so not going to mess with it this trip. Just making sure MY plc is not the issue, I don't think it is.
I suspect, but do not know, that higher speeds results in resolver signal issues, which the drive reads as a fault. A qualified drive person could, perhaps, dumb down the drive a bit, so it can handle these older signals.
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Unread November 19th, 2019, 03:35 PM   #4
Ken Moore
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Just read in the 1771-OFE manual that using BCD and scaling the internal scan rate is 8ms, so I'm okay I think, using 10ms writes.
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Unread November 19th, 2019, 04:20 PM   #5
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The 1771-IFE may be your limiting factor. Its fastest Real-Time Sampling (RTS) period is 100 ms, and according to the IFE-C user manual (1999 rev), the internal scan rate is specified at 13.7 ms/27.4 ms (differential/single-ended). So even though the STI is 10 ms, it might be processing stale input data.

I also recall there is special handling of BTRs in the STI, but can't find a specific reference right now. Something like the instruction completes synchronously in the STI, meaning that it may just return whatever is the latest value in the module's buffer. If you're not getting overrun on the STI, I would question whether it is reading duplicate values from the IFE module at the 10 ms update period, as opposed to fresh updates from the encoder.
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Unread November 19th, 2019, 04:33 PM   #6
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Quote:
Originally Posted by Ken Moore View Post
Now randomly, a new Siemens S120 drive will fault with "encoder" fault. I suspect the old resolver encoder they have on the motor is the issue, but just wanted to brain storm a bit.
Yes, it must be related to the drive feedback device. Even if your PLC analog updates were slow, that could only result in a "stair stepped" analog signal with bigger steps. The only way I can think of that could cause a drive problem is if the drive is attempting too big a speed change (still shouldn't be an encoder fault).

I believe there are status bits even in the PLC-5 that you can check for STI overlap and other status bits for the block transfer buffers to ensure you aren't overloading that process by slamming that channel with 200 block transfers per second (assuming both the BTR and BTW are in the STI).
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Unread November 19th, 2019, 04:38 PM   #7
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Quote:
Originally Posted by Ken Moore View Post
Old equipment, trying to run faster than designed.
I have a client that is still running a PLC5/40 on an extruder line. They are using a 10ms STI to read encoder values BTR and send speed to a drive via a BTW to a local AO card ( not remote IO). The drive powers a "puller" that runs about 10% above the extruder speed. So as the extruder ram changes speeds, the puller has to match.


They have slowly over the years increased line speed by about 50%. Now randomly, a new Siemens S120 drive will fault with "encoder" fault. I suspect the old resolver encoder they have on the motor is the issue, but just wanted to brain storm a bit.
The folks who installed the new drive say it's a plc problem, but supposedly all the problems started with the new drive. No proof of this.

If they slow down the line by about 10%, almost no issues.

Just for my own knowledge, does anyone know how fast a 1771-OFE1 and 1771-IFE can process at?
The speed that the drive is running is one factor, and that can cause an encoder fault. That should be easy to figure out by speeding up the drive with the extruder offline until you get the fault. Or maybe I missed something there.

How fast you can process AI and AO is how fast you can UPDATE what the speed is. ... if I read that correctly. Is the extruder changing speeds 100 times per second? If the puller was to update 50 times per second instead, does the product quality/consistency (diameter of the extrusion maybe?) suffer?
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Unread November 19th, 2019, 05:12 PM   #8
Ken Moore
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The ram speed changes speed slowly, so if I miss an update or two, not a major issue.
Scan time for the STI ladder program is about 6 ms, so should be okay, overall scan timer varies from low 20's to mid 30 ms range.

The drive is only running at about 15% most of the time. Not real fast. The speed reference usually runs from about 14.5 to 16.5 percent, so not a lot of change as it goes down the line. The encoder cable was recently replaced, so must be the encoder "skipping a beat" every once in awhile. On Monday, it faulted 7 times in two hours, then ran fine for 4 hours, no way to predict. Heat, humidity, phase of the moon.
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Unread November 20th, 2019, 02:32 AM   #9
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Could there be interference occurring?
We’ve had Solenoid’s switching etc cause random errors like this before.
That it is intermittent could depend on where the encoder is at relative to when the switching occurs..
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Unread November 20th, 2019, 04:51 AM   #10
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Exactly what is the drive part numbers ?
If it is a newer Siemens drive it probably has a "Control Unit" and a "Power Module".
Depending on the Control Unit, it might be possible to go online and read out the fault codes. There is also a memory of past fault codes.
If it is not directly possible to go online, you can probably get a local operator panel (usually "BOP" or "AOP"). The BOP is very cheap so no reason to not have it.

I doubt that the analog speed input can cause the fault.
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Unread November 20th, 2019, 05:12 AM   #11
Ken Moore
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Quote:
Originally Posted by lostcontrol View Post
Could there be interference occurring?
We’ve had Solenoid’s switching etc cause random errors like this before.
That it is intermittent could depend on where the encoder is at relative to when the switching occurs..
Well it usually faults at one of two locations, in the first one there are clamping solenoids, so that is a possibility. the second location is when it is just pulling down the line, nothing going on.

This is one of those jobs, where I may never discover exactly what is going on, not enough time on site. I will just do the best I can, and recommend the drive contractor come back for monitoring/troubleshooting.
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Unread November 20th, 2019, 05:14 AM   #12
Ken Moore
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Quote:
Originally Posted by JesperMP View Post
Exactly what is the drive part numbers ?
If it is a newer Siemens drive it probably has a "Control Unit" and a "Power Module".
Depending on the Control Unit, it might be possible to go online and read out the fault codes. There is also a memory of past fault codes.
If it is not directly possible to go online, you can probably get a local operator panel (usually "BOP" or "AOP"). The BOP is very cheap so no reason to not have it.

I doubt that the analog speed input can cause the fault.
Control module: CU320-2 DP, don't need the DP, guess it was on hand.
Power module is not accessible.
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Unread November 20th, 2019, 06:19 AM   #13
JesperMP
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The CU320-2 DP has an ethernet port for commisioning and diagnostics.
I think you can get diagnostics with Siemens Startdrive Basic software which is quite inexpensive. Ask your Siemens Support contact to confirm this.

Alternatively you can attach a BOP20 operator panel. Also quite inexpensive.
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Unread November 20th, 2019, 06:54 AM   #14
JesperMP
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Here is a link to free download of STARTDRIVE V15.1:
https://support.industry.siemens.com...view/109760845
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Unread November 20th, 2019, 07:38 AM   #15
JRW
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Jesper
Take a look at your Startdrive…
Do you see a 320-2 DP?

Exactly
Startdrive wont work
Only Starter

Ken- get your "Drive Guy"
Then read him the last sentence in post 2

Last edited by JRW; November 20th, 2019 at 07:48 AM.
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