PLC5 IFE and OFE scaling question

[danielsaii]

Hello everyone, I am migrating a PLC5 program controlling a crane to a siemens s7-1500 PLC, but since i have no experience programming PLC5 I have a question about the OFE and IFE cards.

The IFE analog inputs are scaled from 0 to 4095, and the OFE analog outputs are scaled from 0 to 1200.

I have read the manuals and as i understand this means the input is scaled in 4096 parts from 0 to 10v, and the output in 1201 parts from 0 to 10v.

When the crane is running in automatic the output is given values from 0 to 1200 as necessary, calculated by the PLC.

BUT when the crane is running in manual, the analog input values (analog stick) from 0 to 4095 are transfered directly to the analog output (scaled from 0 to 1200) to the vfd.

Now the question... if i put a bigger value than 1200 into the output, how is this treated? what happens? Or, am i misunderstaing completely whats going on?

Because when the input is at about 2.93v = 1200 counts, in manual the output is 1200 counts = 10v, but as the input grows past 2.93v the counts will grow past the 1200 scaled into the output, at least this is how i interpret it.

Sorry if this is really obvious, I'm not used to PLC5 nor AB.

I wish I had the availabilty to test this on hardware, but i have no acces to a PLC5 neither an OFE card.

Thank you all.

 

[Bit_Bucket_07]

It depends upon the specific OFE module, the on-board jumper settings and the configuration data transferred to the module by a Block Transfer Write to the module in the user program. If I'm not mistaken, the 1771-OFE modules are all capable of 12 bit resolution, and the 0-1200 count scaling that you are seeing reflects a non-standard configuration.

 

[danielsaii]

It depends upon the specific OFE module, the on-board jumper settings and the configuration data transferred to the module by a Block Transfer Write to the module in the user program. If I'm not mistaken, the 1771-OFE modules are all capable of 12 bit resolution, and the 0-1200 count scaling that you are seeing reflects a non-standard configuration.

Yes, I am aware about the 1200 scaling being non standard and the 12bit resolution. I atached some files for reference.

My main question is: what happens if the value written to N56:64 goes above 1200??, which it does (as i understand) in manual mode since the value from the IFE has a range of 0 to 4095 and is moved directly to the N56:64 file

Thank you


EDIT: Added line where move insctruction from IFE to OFE is made in manual mode

 

[Bit_Bucket_07]

Yes, I am aware about the 1200 scaling being non standard and the 12bit resolution. I atached some files for reference.

My main question is: what happens if the value written to N56:64 goes above 1200??, which it does (as i understand) in manual mode since the value from the IFE has a range of 0 to 4095 and is moved directly to the N56:64 file

Thank you


EDIT: Added line where move insctruction from IFE to OFE is made in manual mode

I see... I don't recall what happens when an OFE module receives an out of range numerical reference like that. I assume that it would simply ignore it and hold last value after passing the 100% mark?

I do recall encountering this situation on a GE Genius distributed IO block once. It had 12 bit resolution and a sign bit, and my program sent a number to the output that exceeded by one count the configured max value. It caused the module to see a negative number and effectively set the output to zero.

Unfortunately, I don't have the hardware available to test it, or I would. Hopefully someone else here can test it for you. Best of luck!

 

[danielsaii]

That would be awesome, but since PLC5 HW is so incredibly hard to come by, I wouldn't hold my breath.

Thanks for your help!.

 

[danielsaii]

I see... I don't recall what happens when an OFE module receives an out of range numerical reference like that. I assume that it would simply ignore it and hold last value after passing the 100% mark?

I couldnt get this out of my head, i kept looking through the N files and there is a value out of range being sent to ch2 (N56:65) of the OFE card, and the value at N55:68 = 66 (0000 0000 0100 0010) has bit 1 set to "1", indicating an out of range value on CH2 (all of this from the manual) now i just have to figure out what happens when an out of range value is given, since it is not explained in this manual i have.

Thank you again.

 

[Ken Roach]

This is a very interesting post, and I appreciate you providing so much detail.

I am 90% confident that if the logic moves a value between 1201 and 4095 to any of the 1771-OFE output channels (N56:64-67) that the output voltage will stay clamped at 10.0 volts.

What you describe with the Analog Input value being copied verbatim to the Analog Output when a control loop is in Manual Mode is fairly common. But it's usually done when the min/max scaling and analog-to-digital resolution for both modules is the same.

Yours probably just works by coincidence when the dial stays in the lower quarter and nobody notices the Kp = (4095/1200) = 3.41 proportional gain effect.

I don't know if the 1771-OFE indicates "out of range" when the output value is outside the Min/Max Scaling, or if it's outside the 0-4095 raw maximums.

Your 1771-IFE input module with the MIN=MAX scaling and the negative input values is the weirder part.

 

[Ken Roach]

I think I can explain the 1771-OFE feedback and status.

N56:64 = Ch1. Analog Output Command= 1200
N56:65 = Ch2. Analog Output Command= -32768
N56:66 = Ch3. Analog Output Command= 0
N56:67 = Ch4. Analog Output Command= 0

What I expect is that Channel 1 is outputting 10.0 volts, and Channels 2,3,4 are outputting 0.0 volts.

The Feedback that you're getting for Channel 1 on the 1771-OFE is showing a value of 4095 when the output Command value is 1200, which make sense if Feedback is always in raw numbers and not in scaled values or engineering units.

N55:64 = Ch1. Analog Output Feedback = 4095
N55:65 = Ch2. Analog Output Feedback = 0
N55:66 = Ch3. Analog Output Feedback = 0
N55:67 = Ch4. Analog Output Feedback = 0

Channel 2 has the Overrange flag set because the value being sent to it is --32710 outside of the 0-4095 range that the A/D converter has natively... or because the value is outside of the 0-1200 min/max range.

Poking a value of 1201-4095 into that would tell us, but of course you don't have access to a running system.

 

[danielsaii]

I think I can explain the 1771-OFE feedback and status.

N56:64 = Ch1. Analog Output Command= 1200
N56:65 = Ch2. Analog Output Command= -32768
N56:66 = Ch3. Analog Output Command= 0
N56:67 = Ch4. Analog Output Command= 0

What I expect is that Channel 1 is outputting 10.0 volts, and Channels 2,3,4 are outputting 0.0 volts.

The Feedback that you're getting for Channel 1 on the 1771-OFE is showing a value of 4095 when the output Command value is 1200, which make sense if Feedback is always in raw numbers and not in scaled values or engineering units.

N55:64 = Ch1. Analog Output Feedback = 4095
N55:65 = Ch2. Analog Output Feedback = 0
N55:66 = Ch3. Analog Output Feedback = 0
N55:67 = Ch4. Analog Output Feedback = 0

Channel 2 has the Overrange flag set because the value being sent to it is --32710 outside of the 0-4095 range that the A/D converter has natively... or because the value is outside of the 0-1200 min/max range.

Poking a value of 1201-4095 into that would tell us, but of course you don't have access to a running system.

All of this seems right, also answering some points from your previous post:

Yours probably just works by coincidence when the dial stays in the lower quarter and nobody notices the Kp = (4095/1200) = 3.41 proportional gain effect. and Your 1771-IFE input module with the MIN=MAX scaling and the negative input values is the weirder part.

I even had thought that the analog stick didnt put out the full 10v and that could be the reason for the difference. but the min max scaling did put me off, so i thought there could be something wrong with the card when the program was backed up. i kept looking through the files and found out (sorry!!! this seems obvious now but im not used to AB) that you can configure the BTW instruction through the GUI (attached) and now it all makes sense.

The input card is scaled from -1200 to 1200 volts in a -10 to 10 config (edit: the 7654 on ch1 on max scaling was done by me accidentally and forgot to change it back)
The output card is scaled from 0 to 1200 in a 0 to 10v config.

This was all a non issue to begin with. but hey, it least now im not worrying about it.

Even though i know the reason (old plc) I still find it really weird that there is not a single HW config gui page for all hw, and that it has to be done with the BTR and BTW instructions on everyone of them. I also struggled with a RS232 card and a prosoft card on this same project last week.

Thank you all for your comments