Configuration of 4-20mA sensor with DT9829 using QuickDAQ Software

[Todd]

I have a 30 psi sensor that I have connected to the DT9829 with an external source voltage supplied.  I configured the sensor in QuickDAQ as a current sensor and then used custom units as psi.  For sensitivity I am using 0.001875 but it appears to be too low.  The sensor is 4-20 mA, so 4 mA = 0psi, and 20 mA = 30 psi, or 1.875 psi/mA.  I think the DAS measures current as A instead of mA, so I divided 1.875 by 1000 to get 0.001875.  I am waiting to get a pressure gauge to compare the output to but at the moment the displayed "psi" appears to be much lower than expected.

Let me know if you have any guidance for setting up a 4-20mA sensor using the Current input option on the DT9829 with QuickDAQ hardware.

Thanks,

Todd

[JRys]

Hello,

The DT9829 should return a non-scaled value between 0.004 and 0.020. Each mA will have a PSI weight of 1875. Because 4mA is zero use an offset of 4 * 1.875 or -7.5.

For example, 0.004 * 1875 - 7.5  = 0 psi; 0.020 * 1875 - 7.5 = 30 psi; 0.012 *1875 - 7.5 = 15 psi.

Thanks,
John

[Todd]

John,

Thanks for the feedback.  Based on your example, my sensitivity should be 1875 instead of .001875.  I will give that a try.

Thanks,

Todd

[JRys]

Hey Todd,

Could you also try 1 / 1875 (0.0005333)?

Thanks,

John

[Todd]

John,

I just traveled out to the test site today.  When I tried 1875 instead of .001875, I didn't get any response when I supplied pressure to the pressure transducer, however 1/1875 (0.000533) is a lot closer but appears off by about a factor of 2.  

For the configuration value, I create a custom value of psi.  The mV/EU value is the slope however the measured value should be 4-20 mA.  For current measurement is the value mA or does the DAS internally run the voltage across a resistor and measure the voltage drop in mV?  Trying to understand what units the current measurement is.  The voltage input sensors are much more straight forward.

Thanks,

Todd

[Todd]

I was DT9829 focused on the voltage and didn't double check the Noshock 100 datasheet.  I checked it and it specified a minimum voltage of 10 VDC and when I supply 12VDC, the .000533 value correlates within .2 psi at full scale if I use a large offset.  

I still haven't been able to figure out how the mV/EU conversion works for mA sensors.  If I measure straight current using the DT9829, it appears to be a nominal -20mA and then increase to -4mA.  I thought maybe I had the wires reversed on the sensor and I tried swapping them but then it just rails at -25mA.  I would have expected to measure ~4mA with no pressure and ~20mA at full scale for the 30 psi sensor.

Let me know if you have any suggestions.

Thanks,

Todd

[Fausto]

Hello @Todd.

The default unit for current measurements in QuickDAQ is Amps.  I entered the mV/EU and offset values (0.00053333 and -7.5, respectively) which @JRys mentioned previously and they worked.  (0.004 A = 0 PSI, 0.020 A = 30 PSI)  Please confirm you used both values. 

 

Regards,

Fausto

Edited March 21, 2023 by Fausto
added values

[Todd]

Fausto,

Using the .000533 mV/EU makes sense however for current measurements it should be interpreted as mA/EU.

The offset of 7.5 psi makes sense however I had to use +40.4 and then I would get 0 psi when no pressure is applied and ~29.8 psi when 30 psi was applied.  

When I change the input to mV/EU and 0 offset to use the DT9829 as a current sensor input, I get -0.021 A at 0 psi and -.004 A at 30 psi. I am not sure why this is occurring.  

Todd

[Fausto]

@Todd,

Please share the datasheet of your pressure sensor.  

On 3/2/2023 at 8:34 AM, Todd said:

The sensor is 4-20 mA, so 4 mA = 0psi, and 20 mA = 30 psi

Do you have a multimeter to verify a 4 mA output from your sensor when there is no pressure (0 psi)?

Also, with the input type set to 'Current' and the default mV/EU value as '1', zero pressure should read 4 mA.  Likewise, 30 psi should read 20 mA.

Please reply with your screen captures. 

Regards,

Fausto

[Todd]

Fausto,

I tried that this morning and got the following.  I configured the channel to display Amps and set the mV/EU value to 1 and offset to 0 psi and then compared it to a current meter.

At 0 psi:

DT9829 Displays -0.021A (-21 mA)

Current meter displays -4.1 mA

At 30 psi:

DT9829 displays -0.005A (-5mA)

Current meter displays 20.1 mA

I think the large initial offset required for the DT9829 is because the DT9829 is reading -21 mA at 0 psi.  I would have expected the DT9829 reading to be close to the meter reading or about 4 mA.

Todd

[JRys]

Hey Todd,

It sounds like a wiring issue. Do you have a schematic showing the power supply and how the sensor is hooked to the 9829-8? Is it a two or 3-wire sensor? 

Thanks,

John

[Todd]

The sensor is Noshok 100 series (100-30-1-1-25), which is a 2-wire sensor.  I temporarily added a current meter and I am getting the expected 4 mA when the sensor is at 0 psi and 20 mA when the sensor is at 30 psi, however ithe DT9829 shows a -21mA when the sensor is connected at 0 psi.  I am supplying 12VDC to the sensor and the return of the sensor is connected to CHn+ and CHn- is connected to the 12VDC supply return.

I found this issue only occurs on Channel 0.  The rest of the channels appear to be functioning normally so an offset of -7.5psi results in 0 psi when no pressure is supplied.  Channel 0 appears to have a large offset nominally and I am not sure why.

Todd

[JRys]

Your sensor hook up is sound. However, channel 0 should not have an offset, so I suspect it needs to be repaired.

When you have downtime, we can arrange for service. There will be no charge if it's less than a year old. If outside one year, the repair will be about $540.00 plus shipping. It includes a recalibration.  Unfortunately, our turnaround time is four weeks.

Best regards,

John

[Todd]

I think it might be within the 1 year timeline.  It is serial number 20EEC80.  I had a second unit and at first it had an issue where the sensor reading did not match the pressure.  I think there was a weird bug for Analog input channel 2 where it would not accept the mV/EU input value.  I tried changing it several times.  I was able to resovle it by deleting all the configuration files from the ...AppData\Local\Data Translation and then it would accept the input mV/EU values.  I am using version 3.7.0.49 of QuickDAQ.  Have you seen this issue before?

[JRys]

Hey Todd,

Could you double-check that serial number? Take a picture of the label.

I have seen an issue with QuickDAQ, and the fix was to delete the setup file, so yes. It doesn't often happen, though.

John