Measure Resistance BNC 2090A

[Curt_C]

Hi,

I use a BNC-2120 at my desk when I develop code.  There is an input that uses ai3 and ai11 to measure resistance on the BNC 2120 that works very well and suits my requirements.  How do I make that same connection using a BNC 2090 that doesn't have the switch/connections for resistance

fromthe bnc 2120a user manual

thanks

Curt

Measuring Resistance

You can measure resistance with the analog input screw terminals on the BNC-2120. Figure 4 is a

schematic representation of how the BNC-2120 measures resistance.

Figure 4. Measuring Resistance on the BNC-2120

RES+ is internally connected to AI 3 and VCC. RES– is internally connected to AI 11. There is also a10 kΩ resistor between AI 11 and AI GND.

When connecting signals to the screw terminals, use 28–16 AWG wire with the insulation stripped

to 0.28 in.

Complete the following steps to measure resistance.

1. Move the RES/BNC switch above the AI 3 BNC to the RES position.

2. Configure your software to measure AI 3 and AI 11 in referenced single-ended (RSE) mode.

3. Connect the resistor to the RES+ and RES– screw terminals.

You can measure resistors with values ranging from 100 Ω to 1 MΩ.4. Measure VCC on AI 3 and the voltage drop across the internal 10 kΩ resistor on AI 11.

5. With these measurements, calculate the resistor value using the following formula:

Resistor Value

VAI 3 – VAI 11

VAI 11 ⁄(10 kΩ)

= ---------------------------------------

[Hillman]

Hi Curt,

Good afternoon and I hope your well today.

Thanks for the post. 

As you have correctly identified the 2120 includes the required circuitary to measure the value of resistors. The 2090 does not.

To measure resistors using the 2090 you will need to implement a similar solution. 

Two common methods for measuring resistance are the 2-wire method and the 4-wire method. Both methods send a current through a resistor with a measurement device measuring the voltage drop from the signal before and after it crosses the resistor. The 2-wire method is easier to implement, but this method is less accurate than the 4-wire method for resistances below 100 Ω. To calculate resistance, use the following equation.

R_(Ω) = V_(V) / I_(A)

where R is the resistance, V is the voltage, and I is the current.

For more information on the 2-wire and 4-wire methods please see the below tutorial.

Resistance Measurements

http://zone.ni.com/devzone/cda/tut/p/id/3981#toc1

Note: This mentions DMMs but if you wish to use a DAQ card you can.

I hope this finds you well and please let me know & indicate if this helps,

[Curt_C · Accepted solution]

Hi James,

Thanks for the reply.  I figured out how to configure the hardware on the NI-2090A to measure resistance.

I added a 10K 1% metal film resistor to the input of ai8 (R31) and tied the input of ai0 to 5V.  It works very well.

Set input to SE/RSE and measure 2 voltages

Resistance = (Vai0 - Vai8) / (Vai8/ 10000)

See attached.

Thanks

Curt

[Hillman]

Hi Curt,

Thanks for sharing that. So you employed the solution the 2020 used, just you had to do it yourselve!

Thanks for posting your solution.

No problems helping - I love to help the forums!

Thanks,