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Connect String Pots and Linear Pots to NI 9216

I would like to connect String Pots and Linear Pots to the NI 9216, I am kind of confused as its my first time to deal with this kind of connections. Also all the resources I found was using different modules where the wires are connected to the pins (ground, +5V and AI0).

 

Thanks in Advance

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Message 1 of 34
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Hi askhassan,

 

The NI 9216 features 3 or 4 wire RTD measurement setups.

How familiar are you with RTDs?

 

Essentially the module will pass a current between the excitation and the ground pins, and measure the voltage drop across the sensing pins.

In the case of a "4 wire" measurement, these are 4 separate pins. In a 3-wire measurement, the +EX and +Sens pins are the same (see the diagram in the datasheet. marked RTD+, RTD- and 4-wire EX, COM).

 

To connect variable resistors and measure their resistance it appears the module can directly output the calculated resistance (0 to 400 Ohms) - it does this (if it does this, I haven't tried) by applying Ohms law to a measured voltage given a known (1mA) current.

 

You need to connect one end of your resistor to COM and RTD-, and the other end to EX and RTD+. If you use 4 wires it will in principle be more accurate than if you use fewer - read about RTD measurements for more details.


GCentral
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Message 2 of 34
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Hi cbutcher

Thanks for you reply, really appreciated. 

I am really not familiar with RTDs that's why I thought this module might be chosen from the sales man by mistake to serve what I need to do.

I just do not know if it will be the easiest way to connect 10 String Potentiometers and 2 Linear Potentiometers to the NI 9216, where I should be getting a Voltage output as far as I know (I am completely new to this). 

As far as I understand from you, is that I will be measuring resistance and then I could change it to voltage, how can I get the current value ? also is there a way to directly translate that into the displacement moved by the spring wire or the pot stroke?

 

Thanks again

Ahmad 

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Message 3 of 34
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Hi Ahmad,

 


@askhassan wrote:

I am really not familiar with RTDs that's why I thought this module might be chosen from the sales man by mistake to serve what I need to do.


When you are NOT familiar with RTDs then you should read about them, like here on Wikipedia!

Which requirements did you tell your "sales man" so he chose that module?

 


@askhassan wrote:

I just do not know if it will be the easiest way to connect 10 String Potentiometers and 2 Linear Potentiometers to the NI 9216, where I should be getting a Voltage output as far as I know (I am completely new to this). 

As far as I understand from you, is that I will be measuring resistance and then I could change it to voltage, how can I get the current value ? also is there a way to directly translate that into the displacement moved by the spring wire or the pot stroke?


Nothing of all this makes sense with a NI9216 module. Did you read its manual with all the diagrams shown?

The NI9216 will source its current and measure a voltage drop across a single resistor. It is not made to measure voltage drops across a voltage divider made up from 2 or more resistors! It also only supports 8 channels, not the 12 you want to measure.

Most probably you will need a simple voltage measurement module, like NI9205 - but again: what are your requirements?

Best regards,
GerdW


using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019
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Now I got a NI 9205 Module, I need to connect 5 String Pots and 5 Linear Pots to it. Is it preferable to connect it in a differential way or single ended ? and can I use the same common ground for all of them ?

 

 

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Hi again, 

 

That's really a choice. In general, I'd suggest differential measurements when available and not a problem for channel counts, but if your channels all have a common ground (and you want that) then one of the single ended modes will be more suitable. 

 

This link might be useful for you (you can also check the related/parent topics): Measurement System Types and Signal Sources 


GCentral
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Message 6 of 34
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Hi cbutcher,

 

Thanks again for your reply. Would you mind elaborating a little bit about the connections. I attached the NI 9205 Data sheet, the String Pot sheet and the Linear Pot sheet. I think the NI 9205 has up to 16 channels so count might not be a problem. It is just what would be better for this situation. I am sorry for that but its my first time to deal with DAQ in general so your help is much appreciated.

 

Thanks

 

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Message 7 of 34
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Well, for a potentiometer you have 3 pins - two end pins and a middle pin (on a schematic, physical layout could be whatever).

 

The end pins (1 and 3 on the 9600, 1 and 2 on the SP1) should be connected to your ground and a suitable voltage source (e.g. 5V). The middle pin (2 for 9600, 3 (blue) for SP1) is the one that will vary according to position/extension. You connect this to your AI+ pin on the 9205.

 

You can connect your grounds to AI Sense (NRSE), AI GND (RSE) or AI- ((pseudo-)Differential) depending on the wiring configuration you choose for the 9205.

 

Note that unless you externally are grounding your potentiometers, they are "floating" sources for the purpose of the diagram on the link I previously gave. The power supply can be a way for these to become grounded - take care to ensure that the source voltage (e.g. 5V above) is sharing a ground with your 9205.


GCentral
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Message 8 of 34
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So in my case the signal cables will most probably be long (longer than 10 ft), which connection would yield good results ? Also, do I need to have a power supply for this connection type ?

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Message 9 of 34
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Hi ask,

 


@askhassan wrote:

do I need to have a power supply for this connection type ?


You don't need a power supply because of the "connection type".

You need the power supply to drive your resistors and to get an output signal from them! (After all they are just voltage dividers, so you need some voltage to divide it…)

Best regards,
GerdW


using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019
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