Laser Reflex Sensor Voltage Output Problems

[8Project6]

I am a Civil Engineering student and I am working on a project using a laser sensor which outputs a voltage between 0 to 10V (depending on displacement measured). However, I need to feed the range into a DAQ board (Data Acquisition) and it requires a range of -5V to 5V. Is this any easy fix with a circuit? Or is it more complicated than it seems? Help please, I don't know much in the way of electronics!

 

[ericgibbs]

I am a Civil Engineering student and I am working on a project using a laser sensor which outputs a voltage between 0 to 10V (depending on displacement measured). However, I need to feed the range into a DAQ board (Data Acquisition) and it requires a range of -5V to 5V. Is this any easy fix with a circuit? Or is it more complicated than it seems? Help please, I don't know much in the way of electronics!

hi,
One way that is sometimes used, is to connect the DAQ input to -5V via, say a 4K7 resistor and the [0 to +10V] Laser output to the DAQ also via a 4K7 resistor.

This assumes a low impedance output from the laser, you may have to experiment with resistor values to give the range you you require.

EDIT:
The way I would choose is a operational amp level shifter.

 

[8Project6]

Data Sheet for Laser also gives:
-Current Load Voltage Output: < 1 ma
-Current Output Load Resistance <500 Ohm

Would this imply a sufficiently low impedance?

 

[ericgibbs]

Data Sheet for Laser also gives:
-Current Load Voltage Output: < 1 ma
-Current Output Load Resistance <500 Ohm

Would this imply a sufficiently low impedance?

hi,
If you want the highest accuracy for your application I would recommend a OPA, operational amp.
You would require a dual +/-12V supply and and good OPA, say a CA3140.

If a circuit was drawn up do you have the resources to build it.?

 

[8Project6]

Wow, thanks. Yes, I can buy whatever parts I need from the electronics department here at the university. If could draw something up that would be very helpful.

 

[ericgibbs]

Wow, thanks. Yes, I can buy whatever parts I need from the electronics department here at the university. If could draw something up that would be very helpful.

hi,
I'll post a circuit tomorrow.

Whats your location.?

 

[8Project6]

That would be fantastic. I am at the University of Minnesota, United States.

Edit:
Also, I have been using a +/-12V supply for the laser so that should be perfect.

 

[ericgibbs]

That would be fantastic. I am at the University of Minnesota, United States.

Edit:
Also, I have been using a +/-12V supply for the laser so that should be perfect.

hi,
Look at this circuit, its been tested and it works.

 

[8Project6]

Thanks again. It may be a week or so before I am able to build it but I will let you know for sure. I think I understand how to put most of it together, but what is the Power Rail Filter?

 

[ericgibbs]

Thanks again. It may be a week or so before I am able to build it but I will let you know for sure. I think I understand how to put most of it together, but what is the Power Rail Filter?

hi,
The filter is a way of reducing any 'electrical noise' on the power rails that may cause errors in the application,
it also helps reduce any 'noise' that your application may inject back into the power rails
which could cause problems in other circuits using the same power supply.

Its an essential standard engineering practice to fit on board 'noise' filters to power supply lines.

OK.?

 

[8Project6]

So then, the power rail filter would connect to the +/-12V powering the Op-Amp, on the side where C3 and C6 are? Also, I have 2 leftover 5k pots; could I use them in series instead of the 10k variable resistor?

 

[ericgibbs]

So then, the power rail filter would connect to the +/-12V powering the Op-Amp, on the side where C3 and C6 are? Also, I have 2 leftover 5k pots; could I use them in series instead of the 10k variable resistor?

hi,
You could change the R3 to 8K2 and use a single 5K variable as the Gain pot.

On that feedback path, the 'target' is to make the 8K2 and 5K variable[when adjusted] equal to about 10K total.

 

[8Project6]

Hi Eric,

I bought the parts required and constructed the circuit, but I can't get it to give a negative voltage when between 0 and 5V are input.

I followed the set up instructions and adjusted the wipers to +5 and -5 volts, then connected the laser, and when it fed in 10V the output was +4.1 Volts. I adjusted the first wiper again so the output was +5 volts, but now turning the RV2 didn't do anything. When the laser output 5V the circuit output was about 0V, but it never went negative when less than 5V was output by the laser (into the circuit).

Thanks,
Dan

 

[8Project6]

Anyone have any ideas why this circuit (the one Eric posted earlier) is not outputting negative voltages when below 5V is input? I need it to output -5V when 0V is input and +5 when 10V is input. It works correctly from 5V to 10V input, giving 0V to 5V output. Thanks!

 

[ericgibbs]

Anyone have any ideas why this circuit (the one Eric posted earlier) is not outputting negative voltages when below 5V is input? I need it to output -5V when 0V is input and +5 when 10V is input. It works correctly from 5V to 10V input, giving 0V to 5V output. Thanks!

hi,
Just seen your post, Ill have a look.

Hi Dan,

Couple of questions, do you have +12V on pin 7 and -12V on pin 4 of the CA3140.???

 

[ericgibbs]

Hi Dan,

Couple of questions, do you have +12V on pin 7 and -12V on pin 4 of the CA3140.???

 

[8Project6]

Yes, I have those pins hooked to those voltages, but I just noticed that once I attach the laser the -12V becomes 0V?!! So then pin 4 is attached to 0V and pin 7 to +12V. Do I need to use a separate power supply for the laser? It says it needs a supply voltage of 18 to 30VDC. I have another supply I can use, but it would be very convenient to only use the one supply for transportation purposes.

 

[ericgibbs]

Yes, I have those pins hooked to those voltages, but I just noticed that once I attach the laser the -12V becomes 0V?!! So then pin 4 is attached to 0V and pin 7 to +12V. Do I need to use a separate power supply for the laser? It says it needs a supply voltage of 18 to 30VDC. I have another supply I can use, but it would be very convenient to only use the one supply for transportation purposes.

hi,
It sounds as though you have a psu grounding problem between the laser and the level shift/amp pcb.

I would use a separate psu for the laser.

EDIT:
Can you post a sketch showing how the unit and laser are connected to psu.??

 

[ericgibbs]

Hi
Is this how you had it connected.???

If yes, you cant do that.

 

[ericgibbs]

hi Dan,

The current required by the OPA circuit is low milliamps.

Its possible to use a dc to dc convertor, size about a 1inch cube.

Drive it from the laser supply and use the +/-12Vdc isolated outputs to power the OPA

This is the device.

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