Phidget for DAQ + interfacing 0-10V, 0/24V external sensors

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luneart
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Phidget for DAQ + interfacing 0-10V, 0/24V external sensors

Postby luneart » Wed Nov 02, 2016 4:21 am

Hello,
I'd like to use phidgets to build a data acquisition (DAQ) box. I'm a mechanical engineer, and I don't know much on electronics.

** First question, I have external analog sensors, with 0-10V output, and digital sensors, with 0/24V output. How can I interface those to the SBC? So far, I got there:
- not going with the "voltage dividers" modules as sold by phidget, as I think they are more like bridges to measure a variable resistor ;
- making up a voltage divider, but can I just plug the resistors (1kΩ ?) on the terminal blocks? Should I do something more ... clean? with a pcb etc?
For both signals I just need to divide the tension by 2, so I was thinking of plugging identical resistors between the input channel and the ground, and the input channel and the output of the sensor.

** Second question, I will have a *lot* of sensors, can I plug the usb output of a 1018 - PhidgetInterfaceKit 8/8/8 to the SBC? (I read that the SBC itself is a PhidgetInterfaceKit 8/8/8 plugged to a usb port of a mini-computer, then integrated on the same card, so I guess it's fine... isn't it?)

Thank you!

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mparadis
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Re: Phidget for DAQ + interfacing 0-10V, 0/24V external sens

Postby mparadis » Thu Nov 03, 2016 9:05 am

1) You are correct about our voltage divider boards- they're only useful for sensors that report their data by changing their internal resistance (like force-sensitive resistors or thermistors). You should be able to step the output of a 0-10V sensor down to 0-5V with a couple of resistors. Have a look at this diagram showing a 10V supply being stepped down to 5V. The same principle will work with a sensor, although you'll lose some resolution since your sensor value is being halved. Also keep in mind that Phidgets are only capable of supplying 5V power, so if the sensor also requries 10V, you'll need to provide it with an external power supply. If you have a lot of 10V sensors, I would solder the voltage divider circuits onto a piece of protoboard.

As for the 24V digital sensors, it will be a bit trickier. The digital inputs on the 1072 are active-low, meaning they must be pulled to ground in order to activate. So even if you did step them down to 5V, they wouldn't trigger them. You've have to hook up a MOSFET or some kind of relay to switch the digital inputs of the SBC to ground. Alternatively, the Phidgets 1012 board has 16 active-high digital inputs that can handle up to 30V. Again, if these sensors require a high-voltage power supply, you'll need to power the separately, since no Phidget will provide 24V.

2) Yes, you can plug a bunch of Phidgets into the back of the SBC and read sensors attached to them in the same way the SBC can read sensors from it's own I/O ports. Just make sure the power supply you're using can provide enough current for all of the devices (0.5A max per device).


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