Help me with transmitting voltage over 35 meters

[joefor]

Voltage transmitter

Hi all.

Sorry my english.

I need to control a proportional valve (it has electronics inside to control the solenoids). This valve works with voltage. 6v means the valve is in one direction, 12v center, and 18v at the other direction. The valve is proportional, so any voltage betwen 6v-18v means a specific position.

I need to transmit this voltage across 35 meters (115 fts.) of distance aprox. Galvanic isolation is not a consern right now. The question is how to transmit the voltage. Is a simple voltage buffer (a non-inverter opamp) sufficient, or i require something more complex?
I need to desing electronics, so any commercial voltage transmitter is out of scope.

Ok, that's all. Thanks for yours answers.

joefor

 

[VVV]

Re: Voltage transmitter

Personally, over such a distance I would use a current transmitter, with a current range of say, the typical 4-20mA. At the receiving site you can translate that current back into a voltage and scale the output exactly to 6-12-18V.
This way you do not have to worry about losses in the cable and the way they can affect the valve.

Another method would be to use 4 wires for the valve, two to deliver the voltage to it, the other two used to measure the actual voltage at the valve, although I can see this approach having more difficulaties.

In other situations al this would not be necessary, but seeing that the valve is proportional, I think it is necessary here, or you will have errors.

 

[joefor]

Re: Voltage transmitter

Thanks for your answer.

The valves are only one part of the system. There are some rotational encoders, i can measure the position, so i have a control loop to eliminate the errors.

Your idea about a 4-20ma converter it's very good, but i would prefer a slightly simpler solution at this time.

My question is about the line transmittion. I want to know if i a simple non-inverting opamp configuration would be sufficient, or if i need a more suitable circuit for this purpose for a voltage transmitter. If anyone have schematics would be nice.

Thanks again.

 

[Miguel Gaspar]

Voltage transmitter

The answear of VVV is good, transmitting voltage includes contamination by noise. I don't think that you can transmitt voltage succesfully.

Transmitt current and at the reception use a current to voltage converter.

 

[IanP]

Re: Voltage transmitter

The current loop control would be probably the best option, but for 35m distance you can try to hardwire that valve ..

The 6-18V control voltage is @ what current?
Some industrial proportional valve voltage amplifiers are rated @ 300mA, 600mA, 1.2A, 2A and so on ..

If you need less that 1.5A then I would probably use LM317 voltage regulator with 3 potentiometers: one for upper limit, one for lower limit and one to adjust the control voltage between 6V and 18V, or as required, including voltage drop over the 35m(x2) cable ..

Regards,
IanP

 

[joefor]

Re: Voltage transmitter

Ok, the signal for the valve is 6v to 18v @ 0.25mA to 0.7mA. It's also has to be supplied with 24v @0.17A. It can handle a 5% supply ripple (not the signal).

My circuit has to translate a 0-10v to a 6-18v, and then transmit this voltage across the wire to get the valve. The LM317 is controled by potenciometer, but my control signal is the 0-10v. That's why i'm using opamps.

I can do the 0-10v to 6-18v, but i'm afraid about the transmition.

Note: the valve it's a "SAUER DANFOS" model PVEA.

Thanks.

 

[artem]

Voltage transmitter

if you still hardly need voltage to transmit (not current) then you will need 2 paired wires connected in parallel at the valve side . The one is used for voltage transfer , another for voltage reading and error correction due to first wire ohmic impedance.
For reading better to use twisted pair with diff amplifier on receiving end. Make sure that input impedance is high enough to get low signal drop and low enough for noise reception .

 

[VVV]

Re: Voltage transmitter

Given that the current is sol ow you can try to drive the line directly with an opamp, since the voltage drop will be low.
I would add a resistor (a few hndred ohms) in series with the opamp's output, to make sure there are no problems driving the line capacitance.

At the reception side you should also use a simple filter to remove any HF noise that may be picked up by the line.

 

[joefor]

Re: Voltage transmitter

Ok, thanks. I'm going to do what VVV said. The valve seems to have a very advanced electronics inside, so i think it has filters and stuff like that.
If this don't work i going to put a current loop.

Thanks for your help.

 

[IanP]

Re: Voltage transmitter

You can use VVV's advice and employ an opamp ..

Also, because it is "voltage" control and the control current required by the valve is low, I would add a termination resistor of 1kΩ or less at the end of cable and in parallel with the valve's input (low impedance in the transmission line - cable) ..

Regards,
IanP

 

[artem]

Voltage transmitter

joefor,
what i said was relevant for high current load .

For your case it is not known what kind of input your valve is using - differential or not, input impedance, control signal charactecristic - max rise and fall times and signal bandwidth ...

It is impossible to give a proper and reliable solution if requirements above are not specified.