# Voltage to frequency Converter Circuit

#### viju

Joined Sep 28, 2008
120
With the guidance of members I am learning to build miniature circuits for my application.
Here I have an interesting application,

I am using analog modules in the PLC for acquiring analog signals.My analog input ranges from 0-10Volts or +/- 10 Volts.

My analog module costs around $700 or more for 4 channels.Kindly advice me whether my idea of using a circuit will replace the analog input module. I have to design a circuit which receives 0-10 Volts input signal and convert it into frequency.By this I can connect the frequency output of the circuit to the high speed digital input of the PLC. PLC can respond upto 30KHz input pulses.I hope designing a circuit will not cost me more than$100.

While going through the forum search I found that members have specified XR4151. Will it be a precise one as I am replacing a analog input module.please suggest me will my idea of replacing analog module with the V-F work?

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#### beenthere

Joined Apr 20, 2004
15,819
Have you looked for the term "voltage to frequency converter" on Google. It returns 452,000 hits. Many choices, although the 30 KHz figure is very high. Why would you need such a high conversion frequency?

#### viju

Joined Sep 28, 2008
120
I mean to say that my system is capable of receiving 30 KHz signal.I am worried about the reliability of the system.Because I am replacing a proven system with a alternate method only for cost reduction for future projects.Will V-F work with excellent linearity and repeatablity.

#### scubasteve_911

Joined Dec 27, 2007
1,203
If you're looking for cheap analog input modules, then check out ebay.

Honestly, I haven't a clue of how to replicate the analog input module. The circuit shouldn't be trivial if you know the interface needed.

And you speak of precision without supplying a goal. When you design something, you need to be able to know what kind of tolerances, etc. are acceptable.

Steve

#### viju

Joined Sep 28, 2008
120
OK Steve:

I have been measuring high speed pulses in my PLC in the range of 2 ~3KKz for measuring rpm of a dc motor( 12 tooth pinion) which runs at very high speed.I get an accurate reading ( repeatability for the same motor)of +/- 10 rpm at this great speed.
Everytime when I am asked to build a measuring station ( current, resistance,torque) I select the analog input module and program accordingly.But if I use voltage to frequency converter I can avoid using analog input module.If I get 1.23 Volts output from my transducer amplifier and I will convert it into 1.23 KHz ( or whatever) and feed it to my hig speed digital input of PLC. In both the ways I read the values in the data memory of the PLC and values are going to be #00123. I can easily convert them to the form I wanted.

Please suggest me a suitable method if I am wrong.Because this being a measuring station the product goes directly to the customer after the measurement ( This motor comes into your car).

I have also seen the link given by Bertus, I am not able to calculate the values of the component precisely.I need offset and gain adjustment also in the same ciruit so that I can tune it.

The circuit should get 0-10 Volts output and give 0-10KHz frequency for easy calculation.

#### scubasteve_911

Joined Dec 27, 2007
1,203
Okay, still doesn't make sense.

I have been measuring high speed pulses in my PLC in the range of 2 ~3KKz for measuring rpm of a dc motor
You have been measuring high speed pulses, from a tachometer??? This means that you have access to some sort of incremental encoder. Then, you are saying that you use an analog module?

But if I use voltage to frequency converter I can avoid using analog input module.
What is your primary sensor providing? Analog or Digital? You are being ambiguous.

Steve

#### viju

Joined Sep 28, 2008
120
Steve:

I get the pulses through a optic sensor( digital input).I run the motor at the rated voltage applied.For every revolution I get 12 pulses.Pinion will have crest and trough.I can easiliy configure to get pulse for either crest or trough.I have programmed in such a way that I calculate the number of pulses / unit time through interrupt.Then its just a mathematics to convert into rpm.I have 10~15 systems running in this fashion with greatest accuracy.

Steve hope I have clarified you.I have another system wherein I read the rpm from tachometer which is the one as you said.

[I have clarified that my digital input system is capable of receiving high speed pulses.May it has confused you.Extremely sorry for not elaborating properly]

But for current,resistance,torque measurement I have an amplifier suggested by you people which give 0-10Volts output.Right now I have connected them to analog input module.

#### Wendy

Joined Mar 24, 2008
22,130
The problem I see is the incredibly wide range (0Hz? - 10Khz). If expressed in logarithmic terms it's infinite. That does seem a bit ambitious to me, but I wish you luck.

#### viju

Joined Sep 28, 2008
120
Will this IC help my purpose? Input is 0-10 Volts and Output is 10KHz maximum.Please suggest.

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