0-10vdc simulator

[keithkyll]

This thread is for 4-20 mA, but the schematic in post 10 will work.

 

[lesmar96]

You need to connect the other leg of the pot to the negative of the power supply. To protect the analog input channel from overvoltage, put 7 Kohms of resistance between the plus terminal of the power supply and the pot. You should then see 0 - 10 volts on the wiper. Then connect the wiper to the PLC analog input. Also connect the negative of the power supply to the appropriate terminal on the PLC's analog input module.

Thanks Steve. This is what made the difference. I thought I could just mimick a standard resistor by using a pot and that is why I thought connecting the negative of the pot to the negative of the battery wouldn't be necessary, but it made all the difference. Now it works beautiful simply connected to my meter or to the analog input of the plc. Why is this necessary?

 

[lesmar96]

From my observation, Maxkling, an LED or some other extra load is unnecesary? Once wired correctly, as Steve Bailey said, it works good with no load more than the pot on the circuit.

 

[ASF]

Thanks Steve. This is what made the difference. I thought I could just mimick a standard resistor by using a pot and that is why I thought connecting the negative of the pot to the negative of the battery wouldn't be necessary, but it made all the difference. Now it works beautiful simply connected to my meter or to the analog input of the plc. Why is this necessary?

Basic electrical theory. You always have a complete circuit from positive to negative of your power supply/battery. The voltage will drop proportionally across all resistances in that circuit.

Think of your analog input as a voltmeter (which it basically is). In my super detailed drawing below, in the first instance, you have only one resistance (your potentiometer) and so the complete voltage is dropped across it. So there is 24V on the input of your pot, 0V on the output, and your wiper voltage will range between those two values depending on how much you wind it.

The second instance - how you originally had it - has two resistances in series - your pot, and an air gap. Since the air gap has (effectively) infinite resistance, all the voltage will be dropped across that, and nothing will be dropped across your resistor. So as you can see, both of your analog input/voltmeter leads are reading 24V - which means the difference between them is zero volts.

 

[Maxkling]

From my observation, Maxkling, an LED or some other extra load is unnecesary? Once wired correctly, as Steve Bailey said, it works good with no load more than the pot on the circuit.

Either way works, just have to complete the circuit.

 

[danw]

24V across 100 ohms drives 0.24A.

0.24A * 24V = 5.7W

Any lower resistance increases the current and power that needs to be dissipated.

I suspect the excessive wattage when the wiper was near the zero end somehow shorted the end of the pot to the wiper, making it a fixed resistor.

 

[geniusintraining]

We sell a lot of these

https://www.plccable.com/electrical...t-generator-4-20-ma-0-10-vdc-with-case-leads/

They do both 4-20MA and 0-10VDC

 

[lesmar96]

We sell a lot of these

https://www.plccable.com/electrical...t-generator-4-20-ma-0-10-vdc-with-case-leads/

They do both 4-20MA and 0-10VDC

Just thought i'd post a recommendation for these gadgets. Small, portable, easy to use. Just bought one and like it a lot. Good price too

 

[geniusintraining]

Just thought i'd post a recommendation for these gadgets. Small, portable, easy to use. Just bought one and like it a lot. Good price too

Thank you very much! they are made by a PLCTalk member and he does a great job on them

 

[shooter]

Both legs are to be connected 1 to the +24 Volt side and the other to GND, the wiper goes to your input, before connecting check the value with your Fluke as it must stay under 10 Volt.
for safety add another resistor of 7k to the Plus24Volt.