Wrong Resistance Value Using DAQ970A

[Douke]

Hello, 

Just starting to develop with a DAQ970A (Keysight Data Acquisition System) I encounter a problem concerning the acquisition of measurements.

I connected to my channel (Here 101) a resistor of 100Ohm. My software recovers only 1.0 when I measure 100Ohm (Where 9.0 when I measure 99.9 Ohm). I tried different resolution but nothing changed. I tried and searched on the internet all afternoon but nothing... 😕

Thanks in advance,

[Kevin_Price]

I remember some anomalies when I briefly used one too.  I think I found that the 4-wire measurement mode gave expected results while 2-wire mode was not even close.  I remember suspecting that their suggested terminal wiring for 2-wire mode might be in error, but I also couldn't easily track down good info online.  Since I had 4-wire mode working, I didn't really put much more into it.

So: try 4-wire measurement mode (and physically wire the terminals for it).

-Kevin P

[NIquist]

I've used the DAQ970A and older 34972s for years and never had an issue measuring resistance. 

First thing, ignore your code and get the instrument working.  Unless you can see the right value in monitor mode there's no point in programming anything. 

Second, what card are you using?  The DAQM901 is designed for 2/4-wire measurements and is the basic card for DMM-like jobs.  Is that what you have?

Third, Sorry but are you SURE you are reading your resistor right?  Can you check it on a simple handheld meter?

It could also be a setting like Kevin mentioned.  Be sure you are in 2-wire mode.  Reset the instrument and ensure you can at least read 0 ohms for a short and +Inf for an open circuit.  Then try your resistor standards.  

Main manual is here:

Technical Support: DAQ970A Data Acquisition System | Keysight

[Krapfen · Accepted solution]

Hi Douke,

I strongly suggest you to build your own library for DAQ970A, there are several versions of drivers for DAQ970A, non satisfies me.

The following page describes the details of the SCPI commands for DAQ970A.

https://documentation.help/Keysight-34970A-34972A/OKGC%20-%20ROUTe_SCAN.htm

Good Luck.

FrankenChino

[Douke]

Thanks for all  your reply.

@Kevin

I try the 4w during the journey.

@NIquist

For the first Things the monitor Display 100Ohm (The good value)

For the second things, i use a DAQM901A

For the first Things, the monitor display 100Ohm like my resistance and when no resistance +Overload and 0Ohm in short circuit. And i'm in 2Wire

@Franken Chino I will try this too

[JÞB]

~~~~~Oh, 8-Ball! Does the device respond in engineering notation?~~~

Yes! The String is "1.00030 E+2" 

It's expected for any resistance measurement from a DMM typically Voltage and Current measurements fit as %6f nicely from 5.5 digit DMMs across min range to max range. 0.001ish to 300V and 100ths of milli to 10ish Amps.  But 100ths of milliohms to 100rds of megaohms need engineering notation.

[Douke]

@JpB Yes that's what i think after more research, but in my indicator i only have "1.0" how i'm supposed know it's E+2 (We know it's E+2 cause my resistance is 100Ohm). So  i stopped to use the library and use VISA and it's works good 🙂 

So Thanks you for all  your help i can continue to devellop ^^" 

[crossrulz]

---

@Douke wrote:

So  i stopped to use the library and use VISA and it's works good 🙂 

---

In other words, you were given a bad driver.  Another reason I almost always write my own.  SCPI is easy anyways.

[JÞB]

---

@Douke wrote:

@JpB Yes that's what i think after more research, but in my indicator i only have "1.0" how i'm supposed know it's E+2 (We know it's E+2 cause my resistance is 100Ohm). So  i stopped to use the library and use VISA and it's works good 🙂 

So Thanks you for all  your help i can continue to devellop ^^" 

---

Inside the read VI there will be something that converts the VISA Read string to a numeric.   It probably uses fractional string to number%6f is default.  It should be using fract exp string to Number %6g.  That edit will need to be documented. And since your display is using a "," radix separator you might try %;6g.  Colons and semicolons force conversions from "." and "," when 1M = 1,000,000.000 or 1.000.000,000 respectively. 

[Douke]

@JÞB

In the VI "Measure Resistance" it's not a Visa Read it's only a dll return a Dbl.