Voltage to Temperature convertion problem _ 1560 Hart Scientific Black Stack

[johnsold]

Are you sure the device is working correctly? You expect 107 mV but get either 1.25 V or 14 mV depending on the connections. Clearly something is not working in the way you are connecting the devices.

The fact that the multimeter and the DAQ card/LV get the same results indicates that the DAQ card is probably OK.

I suspect that you may have a grounding issue. Try measuring between the ground on the 1560 and the AI Ground of the DAQ card with multimeter with no other wires connected. Measure both AC volts and DC volts. I will not be surprised if you measure hundreds of millivolts AC.

Lynn

[Sakib001]

Hi johnsold,

I just measured the voltage between the grounds of the 1560 and the terminal block and found almost zero voltage betweenn the two. Could you please have a look at the snapshot of the code and comment on the conversion that I used to get the temperature from the voltage ... just have no idea what is going on ...

[johnsold]

With near zero readings a grounding problem is much less likely.

I looked at the 1560 manuals. If you are using the 3560 Extended Communications Module to get your analog output, you should not need the conversion in the LV program. The analog output is proportional to the reading on the selected channel, not to the voltage on the sensor.

What settings are you using for Center and Scale? What measurment type is programmed for the Output Channel?

Lynn

[Sakib001]

Hi Lynn,

yes, you are right. I am using a 3560 communications module. Please have a look at the snapshots i attached for your convenience. I have the DAQ assistant configuration, the output from the 3560 module and the CB 68-LP terminal block in the pictures.

Sakib

[johnsold]

What you need to look at is how you have the analog output configured on the Black Stack.

Lynn

[Sakib001]

Actually I did not have a look at this Analog Output of the Black Stack before. It is showing a Center of 38 and a Scale of 3. The output is configured to measure temperature. Should I change these values?

The display of the Black Stack is showing a value of 18.8702 degree C; but the code is showing a value of -1.2524.

I have configured the DAQ Assistant to measure a voltage. Is that okay? or should I configure it to measure temperature? or something else?

Please help ...

[RavensFan]

Let's clarify.  Your waveform chart is showing votlages around -1.24 to -1.25 Volts.  You say you are expecting around .107 to .108 Volts.  Obviously you are not getting the voltage you are expecting.  Forget about conversion factors in the math node for the moment.  The problem is in your voltage.   That could mean one of several things:

1.  Your wiring isn't correct.  But you said your are seeing the same voltage with a multimeter when the DAQ card is not connected.  So that is probably not the issue.

2.  Your analog output conversion factors in the device aren't what you think they are.  That seems very likely since you said you didn't look into this before.  What Center of 38 and scale of 3 means, I have no idea.  You need to read the device manual.

3.  Your device's analog output is broken.  Always a possibility.  You'd have to read the troubleshooting section of the manual to see if it can help you determine that.

Also,

Double check your wiring.  The PCI-6023 manual shows pin 68 is ACH0 and you have the red wire connected that.  Good.  It shows pin 67 is AIGND and you have the black wire connected to that.  Good.

But in message 14, you show on your device, you have the red wire connected to GND and the black wire connected to OUT.  That is backwards.

However, in earlier message 10, you show the wires connected correctly at the device.  It probably doesn't hurt anything.  But it certainly doesn't help when you flip the polarity on the signal.  Connect it correctly and be consistent.

[johnsold]

I did not save the manual after I looked at it yesterday. From what I recall the setting you have are probably not what you want. With the Center at 38 the analog output will be zero when the instrument display shows 38 degrees C.  I am not sure about the scale, but I suspect that your results are off scale negative.

Read the instrument manual.  I would probably go back to the default settings and see what that produces. Adjust those settings until you get the desired results on the multimeter. The reconnect the DAQ system and it will likely work.

Lynn

[Sakib001]

I have set the Center and the Scale to their default values of 0.0 and 100 respectively and the output channel is configured to measure temperature. Now, the reading i am getting from the Black Stack is 20.1452 °C and the reading i am getting from the code is 0.around 209961. So, do i need to multiply this value with the scale (100). Then the temperature becomes 20.9961 °C. Still, there are significant varaitions after the decimal point. Do i need to play with the Center and Scale values to get the temperature readings matched? Actually for my research, i need precision upto four decimal points. Is an analog data acquisition able to match the values in the Balck Stack dispaly with those in the code?

While configuring the DAQ, which type of input (voltage, temperature, resistance etc.) should i use? Please reply ...

Thank you ...

[Dennis_Knutson]

Probably just variations due to the low resolution of your cheap DAQ device. Are you taking the mean of all of your samples?

I still don't understand why a $10 USB-RS232 converter is not a better option.