Finer Control of 0 to 10v Analog Input (Logix5000)

I have a 10k Pot connected to a 0 to 10v Analog Input on a ControlLogix 5000 PLC. This Pot controls a conveyor speed. I need finer control of the speed of the conveyor as this is used on a rubber extruder and it is stretching the rubber slightly. We are finding it very difficult to sync the conveyor with the extruder. Is it possible to get finer control on a 0 to 10v analog input? The engineering units are set to 0 to 100.

crawfie69 said:

I have a 10k Pot connected to a 0 to 10v Analog Input on a ControlLogix 5000 PLC. This Pot controls a conveyor speed. I need finer control of the speed of the conveyor as this is used on a rubber extruder and it is stretching the rubber slightly. We are finding it very difficult to sync the conveyor with the extruder. Is it possible to get finer control on a 0 to 10v analog input? The engineering units are set to 0 to 100.

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Which Analog Input Card are you using?

Did you set it up the Analog Card to use a Real/Floating Point?

What kind of Pot are you using? Is it Linear Taper?

Stu....

to add to the above
a 10 turn pot

Also is it a single turn or multiturn pot.
You will get better accuracy with a multiturn pot.

A few options:

- Configure the analog card for raw data instead of engineering units. This will give you a range of (probably) 0-32000 in the PLC instead of 0-100. Check the specs of the analog card to be sure. Of course, the scaling would need to be modified in the program.

- Use a multiturn pot with a higher number of turns. 20- and 25-turn potentiometers are readily available in addition to 10-turn.

use three potmeters all 10 k for example.
now you can set both outer ones to a limit for example 4 and 6 volts.
now you have a potmeter ranging from 40 to 60 %.
I would use a sensor on the rubberoutlet with pulses and whenever there is a pulse move the conveyor for x time.

You should also programmatically constrain the minimum and maximum values to use the full span of the pot. For example, you may in practice only need something like 85.0 to 105.0% of motor base speed.

Definitely go floating point or other higher resolution at the channel and in code.

kolyur said:

A few options:

- Configure the analog card for raw data instead of engineering units. This will give you a range of (probably) 0-32000 in the PLC instead of 0-100. Check the specs of the analog card to be sure. Of course, the scaling would need to be modified in the program.

- Use a multiturn pot with a higher number of turns. 20- and 25-turn potentiometers are readily available in addition to 10-turn.

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crawfie69 said he was using "Engineering Units", of 0-100, which I take to mean he has configured the card to give him this range, rather than scaling to engineering units in the code.

If so, it means that the engineering unit range is 0.0 to 100.0 (REAL data), and not 0 to 100 (INTEGER data).

Your suggestion to change to RAW data, would be a backward step, since the resolution of the integer value is far less than the resolution of the floating point value.


The real problem here is that there is nothing to synchronise the conveyor speed with that of the extruded product, so some sort of "creep" is almost unavoidable. What is needed is some form of closed-loop control, where the conveyor speed is continuously adjusted to maintain the take-up conveyor speed so that it neither pulls the product from the extruder, nor allows it to "sag".

There are several methods that could be employed to achieve this...

A fairly simple approach could be to use photo-electrics or proximity detectors to speed-up/slow down the conveyor slightly to keep the extrusion at a (relatively) constant vertical position.

A more precise control could be to close the loop with PID control, using some sort of ranging device looking at the extrusion position.

Without seeing the equipment, (and I am close enough to visit if needed), it would be hard to advise further.

daba said:

Your suggestion to change to RAW data, would be a backward step, since the resolution of the integer value is far less than the resolution of the floating point value.

Click to expand...

I'm not familiar with how analog inputs are implemented in ControlLogix, but I fail to see how any setting could give you a higher resolution than looking straight at the raw signal. If it's a 16-bit input module, for example, then your raw data range is -32767 to +32767. That's the maximum range and resolution provided by the hardware ADC, period. Any "engineering units" setting, whether floating point or not, is simply doing some of the math for you internally to provide a more useable range.

Agreed - I thought you had assumed he had scaled in the PLC 0-100 (integer).

It does not matter if you scale in the plc code, or on the input card, the math is the same.