how to switching arduino thermistor with visa temperature read ?

[Angs6690]

hello, i am working on my final project to controling temperature,

at first i use a thermistor, and now i want to change it to a thermocouple. i was made the Vi program for it, but i still dont know how to connecting it.

i attached the file down there, and i wanna ask is it posible to swtching number 1 with number 2 as attached in "subs.png" down there

i hope someone can help me

thanks.

[Daikataro]

It seems to me you're using the LIFA, so why are you still using VISA primitives? The easiest way to achieve what you want, is a simple Arduino analog port read, followed by some manual scaling; LabView already has the thermocouple conversion VI built in as a function, all you have to do is provide some data like what kind of thermocouple it is. Remember you can't physicaly measure a thermocouple directly, you need a converter like a Dataforth DSCT47 (which is already linearized btw)

[Angs6690]

hello daikataro, thanks for your response. could you please give me an example to use thermocouple conversion read ? because i still dont understand how it works. and btw i use max6675 as signal converter.

thanks in advance

[Daikataro]

Sure deal, it's pretty simple

You can find it in the Numeric > scaling pallete. It will do all the hard math for you, you only need to provide the thermocouple type, excitation (assuming voltage) and the compensation, all of which can be found in your thermocouple datasheet. It is polymorphic so it will adapt to whatever you input as data source, waveform, array or scalar, I recommend the last one so it can work with Arduino read pin, fill in the blanks with your own specifics and you're all set to go. I would recommend to run it isolated first, and when you're certain it works as you want it to, incorporate into main code.

[Angs6690]

hello dikataro, i already tried your suggestion,

the run arrow is not broke that assuming the program was right, but when i click run, it doesn't show the temperature read.

i attached the program down below.

i hope there is a way o solve this,

thank you very much.

best regards,

Angga

[Daikataro]

Yeah, no wonder it is showing a zero, you connected the voltage read output to the compensation voltage, which is a flat amount found in your datasheet. This snippet shows the right way to wire, the Arduino output goes to the topmost terminal.

[Angs6690]

I still didn't get the measurement 😞

the temperature increasing when cjc voltage increased. sometimes the measurement doesn't worked.

i still confuse where the cjc voltage must be take ?

[Daikataro]

Take a look at this NI article about Cjc voltage

http://digital.ni.com/public.nsf/allkb/E332E1D829059FB5862570AE005066B3

You mention you're using an IC as buffer for the measurement, said IC was manufactured by someone who also must provide a datasheet for it, and in the specs section it must include an example on using it for thermocouple readings, along with the values you need to correctly scale it. Does it do any sort of scaling? Or it delivers the raw voltage? For example a Dataforth B47 delivers a linear signal of 0-5V but the B37 doesn't. Here's a simple example that simulates a type K thermocouple raw reading. 

Also keep in mind the ADC resolution of an Arduino is 10 bits, or 4.9mV so if variations are smaller than that, you might be losing data.