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Using 4 Phidget Button Load Cell Sensors (Phidget Bridge)

Posted: Thu Sep 14, 2017 7:31 am
by StefanP
Good afternoon,
we have four button load cell sensors buyed several time ago, which are connected with a phidget Bridge for single usb port connection.

I would like to develop some read outs with C# and i saw that you have for several products documentation.

My questions:
1)Where i can find the documentation for read out of 4 sensor data connected with phidget bridge?

2)Is the reading unit kg correct?

3)Do the read out communicate with port communication, that i can identify specific sensor each port, send a command to port and read it out with an eventhandler? Or is the communication with Posts/gets and returning json f.e.?

4)Is there a possibility to make a zero presure calibration with a command (tar)?

5)Is a renaming of the sensors possible or they have everytime same specific number in a readout (like an array?)

Thanks for answering my questions



Re: Using 4 Phidget Button Load Cell Sensors (Phidget Bridge)

Posted: Thu Sep 14, 2017 9:51 am
by mparadis
1) Have a look at the code samples for the Phidgetbridge in the language of your choice (The bridge uses VoltageRatioInput). Once you get an idea of how the example works, you can write code to measure four sensors instead of one. If you want to log the data to a spreadsheet, this article shows an example of that.

2) The readings of load cells are in mV/V, which means a small voltage proportional to the larger voltage supply of the load cell. In order to convert this number into kg, you need to calibrate using a known weight. For example, measure the mV/V with no load, and then with a known 1kg weight. Then you can use linear interpolation to convert from mV/V to kg. You can use multiple points of calibration to make a more accurate conversion function.

3) You can get the data by either calling the getVoltageRatio method, or by setting up an event handler for VoltageRatioChange. Check the API documentation for your language for exact naming.

4) I don't know what you mean by zero pressure calibration. Do you mean like a "tare" button on a scale? This would be possible, just measure the current mV/V and create a negative offset that is added to the incoming sensor data.

5) The load cells have no memory on them, so the only way you can tell them apart is which channel on the 1046 they are plugged into. If you use setChannel before opening the VoltageRatioInput object, you can set each object to a specific channel ( 0 to 3).

Re: Using 4 Phidget Button Load Cell Sensors (Phidget Bridge)

Posted: Fri Oct 06, 2017 4:34 am
by StefanP
What was the correct unit for the gotten value of the sensor?
is it volt?
Because i get a very small floating number and before tests i thought it is mV.

Re: Using 4 Phidget Button Load Cell Sensors (Phidget Bridge)

Posted: Fri Oct 06, 2017 7:40 am
by mparadis
VoltageRatio objects return a value between 0 and 1, which represents the ratio of how much voltage is being returned compared to how much is being supplied to the sensor.

For example, the Phidget Bridge provides 5V to the load cell, and the load cell sends a small voltage (a few mV) back as its measurement. At any given time, the 5V supply is not exactly 5V, (it may be 5.02 or 4.97V) so the Phidget makes note of this and uses it when it reports the voltage ratio. If the number you get back is 0.001, then you can assume that the Phidget is providing about 5V; 5x0.001 = 0.005V or 5mV.

That being said, the units returned by the Phidget Bridge are sort of irrelevant because either way you'll need to calibrate it with a known weight, so whether you do this with a number in mV or a voltage ratio number will make no difference (in fact the mV number is less accurate because you have to assume the supply is 5V).