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DAQ sensor simulator, help please?

fezz

Jul 5, 2012
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Hi everyone
nice to be a new user in this forum! its great,, thank you guys for such a great help.

I have recently got a new DAQ (data acquisition card) and would like to try it out, however I am not very strong with electronics, so how can I simulate a sensor (pressure sensor, temp. sensor, magnetic sensor… etc.)?
I know that I have to build my own electronic circuit and take out the sensor feedback signal and put it to the DAQ board. Does anyone have a circuit design where sensors are used which I can build and use?
I know it’s a pretty stupid question but I have left electronics for a long time and don’t seem to remember how to get back to it,
I would greatly appreciate if someone could help me or guide me if I am not in the right lines.
Kind regards
Fezz
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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Your post isn't clear: do you want to actually connect sensors to your DAQ board, or simulate them?
You can easily simulate a sensor using a potentiometer. Your DAQ board probably accepts a current or voltage with a defined range, e.g. 4~20 mA or 0~5V. You just need a voltage rail (which may be available on the DAQ card connector already) and a potentiometer to generate a voltage or current in the right range so you can simulate a sensor by turning the potentiometer shaft.
If you want to use an actual sensor, you may need to make up a circuit to interface the sensor to the DAQ input. I've used small four-terminal pressure transducers, which need an op-amp circuit to convert their outputs into a voltage suitable for connecting to a DAQ card. This circuit needs a power supply, typically at least +9V if you want 0~5V output, and possibly a negative power supply too. Other types of sensors will probably need some kind of interface circuit too. Often the manufacturer's data sheet for the transducer will include suggested interface circuit designs.

To start with, tell us the make and model of your DAQ card, and of any transducers you want to interface to it.
 

fezz

Jul 5, 2012
3
Joined
Jul 5, 2012
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Hi KrisBlueNZ
Thank you very much for your post it has certainly cleared a lot of issues to me. I would like to learn both ways please, using a potentiometer and by building a sensor circuit and connecting it to the DAQ. The DAQ I am using is a (National Instruments DAQ Pad 6016 USB Device) here is a link to it,
http://sine.ni.com/nips/cds/view/p/lang/en/nid/14041
Things I would like to connect to the DAQ are pressure sensor, temperature sensor, liquid level sensor, flow sensor and position or switch sensor. If I can make a potentiometer simulator for these then that would be great but if I could build a circuits with actual sensors in it then that would be even better!

Thank you very much for your help

Best regards
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
8,393
Joined
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OK I've had a look at the documentation for that DAQ device. The first 18 pins of the first 50-pin IDC connector are used for the 16 analog inputs. Pins 1 and 2 are analog ground, and need to be connected to the ground rail of your external circuit. Each input has a range of +/- 10V relative to analog ground. You have to provide that voltage externally, so you'll need an external power source for your interface circuitry.

The DAQ inputs have 16-bit resolution and are signed. This means that when you interrogate the card through the NI driver, your software will get 16 values, one for each analog input, and each value will be 16-bit signed. The value you read will correspond to the voltage that you're feeding into the corresponding analog input. Approximate mapping will be:
+10V into pin = 32767 seen by software
+5V into pin = 16384
0V into pin = 0
-5V into pin = -16384
-10V into pin = -32768

You can use the inputs as unipolar (use only the 0~32767 part of the scale, with only positive voltages) or bipolar (-32768~32767 range, with positive and negative voltages). In most cases, probably unipolar will be simpler in terms of the interface circuitry required.

To drive the inputs from a potentiometer, all you need is a source of +10V and -10V (or just +10V). Connect the ends of the potentiometer to the voltages, and the wiper to the input terminal. A potentiometer value of 10K will be fine. That will allow you to vary the values received by the DAQ inputs.

To use real sensors, you will need to make up circuitry to interface each sensor to the DAQ input. This circuuitry will need at least a positive power rail of around +15V and possibly a negative supply rail too. You will need to adjust the gain and/or offset of each circuit so that the output voltage (that feeds into the DAQ module) fits within the desired voltage range, and a particular quantity of the thing you're measuring (e.g. pressure, temperature etc) will produce a specific voltage and therefore a specific digitised value seen by your software.

The interfacing circuitry will be different for each type of transducer, because they all have different electrical characteristics. When you've chosen the transducers you want to use, you should find that the manufacturer's data sheets for the transducers will have a recommended connection diagram, which may include circuitry, to produce a variable voltage from the transducer.

That should be all you need. If you have problems with this part, post again with part numbers for the transducers you want to use.
 

fezz

Jul 5, 2012
3
Joined
Jul 5, 2012
Messages
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Hi KrisBlueNZ
thats great information! i will try it and post again for the results and how it went,,
thank you very much for your help,, i am so glad i registered here,, its GREAT :D

Thanks once again KrisBlueNZ

best regards
 
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