instrument for potentio meters

Hello guest,

Sounds interesting but I'm not getting what you mean by "cut-off point for the linear scale".

If I may hazard a guess, you want to control the position of the hydraulic cylinder using the rotary potentiometer. The linear potentiometer is mounted on the cylinder which gives you feedback of the actual position of the cylinder. Is this correct?

I'll bet a pound to a penny they are not 5 ohm.... 5k, 50k ? maybe.

Thanking U Sir,

Exactly, when set point (Equally divided say 1-10position,and rotary is at 3 set position) of rotary pot reaches of linear pot 3set point. It should send the signal to solenoid valve.

If I understand correctly, you want to use a rotary pot to control where the hydraulic cylinder stops, and the linear pot to determine where the cylinder is located. You simply need a comparator chip like the LM311 (or 111 or 211 depending or precision and reliability required). You connect the slider of the rotary pot to one input and the slider of the linear pot to the other input. The output flips high or low depending on which pot is at a higher fraction of its scale. Better use a multi-turn rotary pot to get the required precision.

If you don't want to build a circuit, you can use two analog in puts to a PLC etc...

I'm not at all sure that a linear pot has sufficient precision to continue stopping the crimping action at the correct position over the long term - depends on the linkages between the cylinder and the actual crimping mechanism.

Thank u sir,

i have connected potention meters by PLC ALLEN-Bradly with PCB and transformer to convert ohms into Volts. but here the problem is converting the Ohms into Volts had became a big circuit. can i have simple one....

Why build?

You can buy resistance-to-current converters for no hassles at all. All you need to do is connect the potentiometers to the resistance inputs and then connect the 4-20mA output to the analog input of the PLC. After connecting power to your converter, your programming does the rest.

First, let me say that Vulcan's solution is more robust than what I am about to say, but the following is probably cheaper:

If you don't need isolation of the sensors from the PLC, and assuming that your potentiometers (single word) are 5k Ohm, not 5 Ohm, you simply connect a 7 kOhm resistor, or a 10 kOhm trim pot adjusted to 7 kOhm, in series with each of your 5k pots, and connect those to the 24VDC supply. This drops the maximum voltage of the two pots to 10VDC, so the sliders can be directly connected to the 0-10V analog inputs of the PLC.

Of course it would be preferable to use a voltage regulator to prevent variations in the 24V supply from reaching the pots. In this case the series resistors would have a lower value, or be eliminated entirely if the regulator output is 10V.

If you need a circuit I could draw one...

Dick

Oh, my myopia!

Dick, thanks. I didn't see the 0-10V requirement. Well, I read it but it didn't register.

Your solution is fine and takes into the account the problem of distance between the potentiometer and the PLC input. The problem with using voltage inputs is that as the distance to the analog input increases, the voltage drop may seriously affect the level that reaches the input module. Having the 7k ohm trim-pot allows him to compensate for the drop.

Hi Vulcan!

Actually the post says "(Equally divided say 1-10position". It does NOT say 0-10V. Its just that that's what I've used on all my machines, because my motion controllers have 0-10V inputs built in, and my control pots are in the same metal enclosure as the controller, so the distances are short and everything is shielded.

Dick

Yes, but in post #5 he mentioned that he was converting resistance to voltage.

Right you are!

It sounds like this is probably for an industrial application. If so, then perhaps a digital encoder along with a uP interface (can be simple) // or even more simply a D/A interface and a comparator (LM311 suggested earlier) to establish the desired end points. This would be much more reliable.

Potentiometers can with time suffer from being erratic and resulting in failure for the task.

Law, Law, Law. Ohm's Law, that is. Use a different voltage on the potentiometers. If you don't get the concept, find someone who does.

This sounds like a lot of effort without any real advantage gained. Whats the point in measuring displacement when performing a crimping operation? Unless your also measuring the force applied, displacement gives you no added value. The two combined can give you the most accurate crimp for any individual part by zeroing out variations in hardness & stackups(dimensions), but without force being measured, it is much simplier just to make a hard stop with a down position switch & focus on keeping the stroke length consistant(If operated manually).

I say this as someone who has spent many years delevoping & improving crimping stations used in crimping pressure sensor housings while also setting the compression of the main seal rings within a tolerance of 2-3thousandths.