MCC USB-2408-2AO - "Steps" in Temperature mode, not in Voltage mode in DAQami or Labview+instacal

[slc]

Hi

When reading in 2 channels of the USB2048 (both with k-type TCs attached). If I set the channels up in temperature mode, the readings have these discrete jumps in them. In voltage mode, the readings are just continually varying as the process temperatures oscillate. 1.png is long term temp mode showing disctete jumps, 2.png shows the jumps more clearly over a short time span. 3.png shows the channels set up in voltage mode, showing no discrete jumps. 

Any idea on where the discrete jumps are coming from in temperature mode?

Thanks

 

[Fausto]

Hello @slc.

If you were not using DAQami, I would suggest configuring the USB-2408-2AO device in InstaCal as shown below.

 

In DAQami, select only those input channels with a sensor and configure each channel similarly to what I set in the InstaCal screen capture above.

 

Most of the noise issues on this board can be solved by lowering the data rate for a noisy channel. This will give the A/D more time to sample the channel. Typically, this simple configuration can solve a noise issue on this board; also helps solve issues with a high source impedance or a very low voltage signal on the analog input channel. Thermocouple readings are typically the most affected by this change, and it is recommended for most applications to be set to 60Hz or below. The lower you can go with this the better. Note that this will limit the rate at which you can capture data. To calculate the maximum scan rate, use the formula 1/fmax = (640 μsec + 1/f1) + (640 μsec + 1/f2)+ ... + (640 μsec + 1/fn) , where n is the number of channels with a data rate fn. More information is available in the USB-2408-2AO user's guide, under the section "Noise filtering, data rate, and throughput rate".

Keep thermocouple wires as short as possible to prevent outside interference and do not allow the thermocouple ends to make direct contact with a metal surface during an acquisition; use an epoxy or thin film tape on the ends.

 

Regards,

Fausto

[slc]

On 5/24/2024 at 2:44 PM, Fausto said:

Hello @slc.

If you were not using DAQami, I would suggest configuring the USB-2408-2AO device in InstaCal as shown below.

 

In DAQami, select only those input channels with a sensor and configure each channel similarly to what I set in the InstaCal screen capture above.

 

Most of the noise issues on this board can be solved by lowering the data rate for a noisy channel. This will give the A/D more time to sample the channel. Typically, this simple configuration can solve a noise issue on this board; also helps solve issues with a high source impedance or a very low voltage signal on the analog input channel. Thermocouple readings are typically the most affected by this change, and it is recommended for most applications to be set to 60Hz or below. The lower you can go with this the better. Note that this will limit the rate at which you can capture data. To calculate the maximum scan rate, use the formula 1/fmax = (640 μsec + 1/f1) + (640 μsec + 1/f2)+ ... + (640 μsec + 1/fn) , where n is the number of channels with a data rate fn. More information is available in the USB-2408-2AO user's guide, under the section "Noise filtering, data rate, and throughput rate".

Keep thermocouple wires as short as possible to prevent outside interference and do not allow the thermocouple ends to make direct contact with a metal surface during an acquisition; use an epoxy or thin film tape on the ends.

 

Regards,

Fausto

Thanks Fausto

I can certainly try some of these, however acquisition rate makes no difference, the step-jumps happen at 10Hz, 60Hz or multi-kHz. 

What is more confusing to me though is that if I look at the voltages directly, the steps are either not present, or are just much smaller than the noise and the conversion from volts to degrees is then quantized to the point that it is jumping between two conversion levels..

 

The following screen shot its 2 identical TCs placed adjacent to each other, one in voltage mode and the other in temperature mode.

 

Thanks
S