Amplified signal - Thermocouples - Conversion ?

[Galjuntur]

Hello, I have another question about reading amplified signal from thermoocuples. My thermocouples ( type K ) will have amplified signal by 100 times. The thing is, I'm unable to use built in option in daq assisstant to get the proper reading. Because of amplifiers ( external ones with differential measurment with three leveled low-pass filter with the cut at the level of 10 Hz ( circa ) ), my thermocouples will work as single ended (SE). 

My question is : Am I able to get temperature reading in a simple steps ( daq assisstant ) or should I use voltage type of signal acquired and then use some sort of conversion ?

I'm looking forward to seeing any reply 🙂

P.S. I found the block -> Convert thermoocuple reading. Should I use it on every channel or can I just wire it in some way to the daq output ?

[Joe_H]

I would bring it in as a voltage and do the scaling and then set up a conversion. You could also do away with the daq assistant (right click on assistant and generate code). Then use the convert thermocouple reading VI you mentioned to scale your values accordingly. Then write it to a file.

Here is what I mean

[Galjuntur]

So I understand that I can just plug the data wire to Convert Thermocouple block and then directly to my signal splitter, right ? Scalling ( in my case 100 x gain ) can be done by dividing block with a value of 100 ?

I'm looking currently for a solution to seeing if the temperature progression is not higher than 1 degC per hour. Is it possible to somehow see the temperature progression in real time ? ( for example to see comparatively the progression between the last hour progression and the present one ? Or the difference bewteen the chosen temperature/time and the present one. I don't know If it's clear.

[Galjuntur]

I'm sorry for double posting but is this conversion possible in my structure or should I do it like u did ? I'm new to LabView and I still haven't figured it out how to implement this to my program. What's more, the scalling for the voltage reading e.g. y=0,01+0 doesn't work.

Error with the scalling :

Requested value is not a supported value for this property. The property value may be invalid because it conflicts with another property.

Property: AI.Min
Requested Value: -10.0
Possible Values: -100.0e-3 to 100.0e-3
Channel Name: Voltage_0

Are the possible values too small or what ?

[sprzysta]

Hi

-100e-3 = -0,1

100e-3 = 0,1

Your value 0,01

Try one of the possible vallues and please write a feedback.

Regards

[Galjuntur]

Right, but the thing is, I cannot eliminate my external gain by this internal scalling. So I added a block ( divide ) and connected a value of 100 to it like in the attached program. I still don' know if I will get a proper readings due to the possible data conversion issues.

[Henrik_Volkers]

One point not mentioned until now 😉  : How is the Cold Junction Temperature included in your conversion?

[Galjuntur]

Well, I forgot about it 😮

I got two possibilities :

a) using constant value ( which is not connected yet - i don't think that cjc voltage = cjc temperature)

b) using one thermocouple as a cjc sensor

[sprzysta]

Hi Galjuntur

Could you write what is the actual status of Your issue?

Im asking because Your last post don't tell me You still have problem or not 🙂

Please write info what is the problem status right now and how We can help You 🙂

Regards

[Galjuntur]

Hi sprzysta,

my current problem is with this temperature conversion. I tried to put the conversion right after the daq assisstant but it turned out that I'm getting only two readings, for channel 1 and 11. ( first in the line ) So it seems that I need to apply such conversion to every channel so I will have 1D waveform for every channel. I am not sure if this is going to solve my problem of getting only readings for two first channel.