Liquid J-Type Thermocouple not Showing Correct Value in DAQami

[Mackenzie Cox]

I have these liquid thermocouples:
https://www.mcmaster.com/1245N27/
Which I previously had hooked up and working fine. Recently, all of the thermocouples of this kind that are hooked up to my DAQ (USB-2416) have stopped working. All other thermocouples are working fine, and when testing these thermocouples with a multimeter, I know they are working find and giving reasonable readings. Any idea why they would have all just stopped working in the DAQ?

[Fausto]

Hello @Mackenzie Cox.

Please elaborate "stopped working".  What are the readings in DAQami for those thermocouple connections?

You mentioned that those liquid thermocouples did work initially.  What changed on your end, i.e. disconnected thermocouples from the DAQ's screw terminals?  Try resecuring the liquid thermocouples to the screw terminals.  Do you have another USB-2416 device to test with the liquid thermocouples?  Do you have other new liquid thermocouples to swap in and test?

Regards,

Fausto

[Mackenzie Cox]

They were giving very wide ranging negative temperatures (they should be, and have been, consistently reading something between then 70-80F range). I unplugged everything except these liquid thermocouples and they started working again when the flow rate sensors I have hooked up to the counters were unplugged. So when I plugged the flow sensors into the counters yesterday (CTR0 and CTR1), all of the liquid thermocouples stopped working... Any ideas on how to fix this?

[Fausto]

So "stopped working" refers "very wide ranging negative temperatures", is that correct?  Are the flow sensors externally powered?  Are the flow sensors connected to the 'CTR#' and 'GND' terminals?  Please provide a datasheet for the flow sensors.

If the tips of the liquid thermcouples are in contact with a metal surface, please use an epoxy or thin film tape (Kapton) at the tips.  Next, try adding a 100 kOhm resistor from the 'CH#L' terminal to an analog ground 'GND' terminal.

[Mackenzie Cox]

Yes, that is correct. The flow sensors are connected to an external power supply. They are connected to green to CTR#, Black to 24V-, Red to 24V+.

Here is the info on the flow sensors:

https://dwyer-inst.com/PDF_files/F_40.pdf

https://dwyer-inst.com/products/flow/flow-transmitters/paddlewheel-in-line/seriessfi-100t.html

The thermocouples themselves are working fine, it is just the DAQ that is having trouble reading them. I attached the 100kOhm resistor to GND from one of the thermocouple CHL. I am still running into the same issue.

Edited August 11, 2023 by Mackenzie Cox

[Fausto]

@Mackenzie Cox,

Do not use the green lead for this application.

Connect the white lead to the 'CTR#' terminal. 

Connect the black lead to your VDC supply's ground.

Connect the red lead to your VDC supply' positive lead.

Retest the new wiring configuration.  Do the liquid thermocouples report correct temperature readings?  If not, then tie the flow sensor's black lead to the 'GND' terminal on the USB-2416 and then retest.

 

[Mackenzie Cox]

Connecting the white lead instead of the green gives me the same issues with the thermocouples and on top of that the flow sensors don't work in this configuration. I also tried connecting the black wire to the ground terminal on the USB 2416 with both the green wire configuration, and the white wire configuration, neither of these resolved the issue.

[Fausto]

There may be an issue with the flow sensor.  Also, by connecting the green lead to the 'CTR#' terminal, if the supply voltage connected to the red lead exceeded +/- 20 VDC, then it may have damaged the USB-2416, since the green lead's voltage equals the red lead's supply voltage.  The white lead should be connected to the 'CTR#' terminal and the green lead disconnected.  The black and red leads should be connected to your external voltage source.  

If you are using a laptop, retest my wiring configuration with and without the external power supply connected to the laptop.

[Mackenzie Cox]

I thought the USB-2416 was fine up to 24V? I am almost certain there is not an issue with the flow sensor, as it works great, so long as the green wire is connected.

[Fausto]

Does the USB-2416 report incorrect readings if the green lead was swapped out for the white lead, connected to the 'CTR#' terminal?

What was the external voltage level on the red lead?  Can you retest with the external voltage level set to between 8 VDC and 15 VDC?

Is the external voltage source connected to the same electrical outlet (or power strip) as the computer or laptop?

If you are using a laptop, retest my wiring configuration with and without the external power supply connected to the laptop.

 

 

[DAQman]

I don't recommend using the green signal wire. Use the white wire instead because it outputs a 0-5v, 0 - 100hz pulse. Power it with +24vdc to the red lead. The black lead is ground.

The counter input is compatible with signals up to 15 volts, the trigger threshold is approximately 1.5v.

If you can read the thermocouples with the flow sensor disconnected but not when it's connected, then you may have a ground loop between the flow sensor 24vdc power supply and the thermocouple probes. The solution is to get isolated thermocouple probes or use an isolated power supply to power the flow sensor.

Another solution would be to use 8B47J thermocouple isolation modules from www.dataforth.com. They isolate the thermocouple and output a linear voltage proportional to the temperature range. 

[Mackenzie Cox]

Even when I connect the white wire to the counter, the other sensor values diverge to incorrect values. Is there a way I can use these flow sensors without using the counter?

When I connect them I can get a voltage, but I have no idea how to interpret the voltage I am getting in terms of flow rate.

[DAQman]

It appears the flow sensor creates a ground loop with the thermocouples, which is why you can not measure both simultaneously. The solution is to isolate the flow sensor and the best way to do this is with a frequency-to-voltage converter. The nice thing about these converters is that they output a linear voltage signal proportional to the flow sensor frequency. It will also allow you to use an analog input instead of the counter input. An example of one that has isolation is the Dataforth 8B45-01. It is rated at 0-500 Hz and outputs a 0-5 volt signal (https://www.dataforth.com/8b45-01). You'll need an 8BP02 back panel and power supply to use it. (https://www.dataforth.com/Search/Results?q=8bp02)

Your flow sensor outputs a 0-100Hz frequency signal. If you use the 8B45-01, 0-1 volt equals 0-100Hz. In other words, you would only need to multiply the measured voltage by 100 to get the frequency. From there, you can determine the flow.

[Mackenzie Cox]

We have a spare power supply. Earlier you recommended trying to power the flow sensor independently from the other sensors. Would you recommend trying that first before buying the frequency-to-voltage converter?  Would we just connect red to that positive supply, black to the negative supply, and then the white/green wire to the counter? Do we need to ground it to the DAQ somehow?

[DAQman]

You will need a power supply that has (+), (-), and (GND) terminals. These three terminals imply that the output is electrically isolated from the earth's ground. Usually, the terminals are colored red, black, and green. If this is what you have, use only red and black. Connect red to red (sensor), black to black (sensor). Connect black to one of the USB-2416 GND terminals and connect the sensor white lead to the counter input. 

Now before you do this, let's consider the measurement. The USB-2416 counter input counts input pulses. For example, if the frequency is 100 Hz, after 10 seconds, the counter will return 1000. For your application, you need frequency because it is equivalent to flow. If you have the appropriate software, it may extract frequency by determining the number of pulses that occur over a set period. For example, 100 pulses in one second is 100 Hz. What software application do you intend to use?

[Mackenzie Cox]

Okay, I will see if that works. And I use Lab view.

[Mackenzie Cox]

I went ahead and bought the frequency isolation module. How do I connect this with the DAQ and my flow sensor?

[DAQman]

Mount the 8B45-01 on the 8BP02 and attach +5 volt power. The flow sensor connects to the side of the board with fewer screw terminals. 

The other side of the board is the output side. It has four terminals, and two are not used (upper). The lower ones are the output and should be marked (+) & (-) or (+) & COM. Connect the (-) to the 2416 GND and the (+) to a single-ended input. If you need clarification on the output, use a handheld voltmeter to determine (+) and (-) before connecting to the 2416. If you're using differential inputs, you can convert the input to single-ended by grounding the low side. 

The 8BP02 data sheet: https://www.dataforth.com/media/pdf/8baccs.pdf 

 

[Mackenzie Cox]

How is the flow sensor connected to the board? Just the white wire to com? What about red and black?

 

[Mackenzie Cox]

Can you try to help me understand why the counter channels and the rest of the high and low input channels cannot work at the same time? Is this something in the DAQ system itself, or something on our end somehow? It is not intuitive how to connect the sensor to the back panel or the back panel to the DAQ system, and I feel like the flow sensors should work in the counters with everything else.

[DAQman]

You can read all the inputs at the same time. Start a new DAQami configuration and enable analog, digital, and counter inputs. Use a Scaler display and drag over the channels. Set the sample rate to 10 and press play. The digital and counter channels are not part of the analog scanning system and aren't as fast as the analog inputs.

The critical thing to know is that the counter channel will not return frequency. So, there is no way to make the flow measurement. If you are having trouble wiring the 8B45 backplane, please get in touch with Dataforth. They can tell you which screw terminals are for the flow sensor and which one is the output.

 

[DAQman]

The following picture is the 8BP02. The output signal is connected to a USB-2416 analog input, such as CH0. If the input is in differential mode, connect CH0L to GND. Connect the Outputs (-) to the USB-2416 GND terminal. Connect the Output (+) to the CH0H terminal. Configure the CH0 to measure voltage using the 5-volt input range. If you can, turn on something so there is flow and verify that you get a voltage. Multiply the voltage by 100 to get a frequency (f). GPM = f / 2 or f / 1.5

[Mackenzie Cox]

I had issues getting this working so we had to order another one. In the mean time, if this does not work, do you have a recommendation for a flow sensor that can work just out of the box, without the need for the frequency isolation module and additional items?

[DAQman]

We don't offer a device with a counter input capable of measuring frequency and analog inputs for thermocouples. 

[Mackenzie Cox]

Do you have a recommendation for just a flow meter that will work with the normal channels, not the counter input?

[DAQman]

The lowest-cost item we offer is the USB-CTR04. It is 5-volt TTL compatible and can be used with DAQami to measure frequency. Use the flow sensor output that is 5 VDC out pulse. 

https://digilent.com/shop/mcc-usb-ctr-series-high-speed-counter-timer-usb-devices/