The ability to measure temperature with the USB 6008?

[rockarmatte]

Hi everyone! I am very satisfied with my USB 6008, except for the possibility of measuring temperatures.

Therefore, I was wonder if it is possible to measure temperatures by 1 degree Celsius accuracy with my USB 6008 and if so, what kind of sensor should I use? As I understand it is so is not an option to use thermocouple as the accuracy is about 10 degrees celcius.

I want to measure temperature is the area of 0-200 degrees C. approximately!

Thanks for your help!

Best regards

/Mattias

[Henrik_Volkers]

How much additional parts are allowed?

Since the board is low cost, the sensor too?  

One or two point calibration possible?

A 2-10k NTC plus additional R in the same range for a voltage divider at the 5V supply with a two point calibration should bring you to 1K in the mentioned range

Cheap and also prone to a one point calibration: Diode voltage measurement (here a improved circuit for longer wires)

Often the application will call for a specific type of sensor..

A good and cheap reference meter (in a limited range 😉  ) is a clinical thermometer 

[rockarmatte]

Hello Henry and thank you for your reply.

Yes, the USB 6008 is a cheap and simple equipment, but the sensor doesn't need to be extremply cheap (preferably cheaper than 100 Euro). I would appreciate it if there is any instrument that does not need calibration points (such as ice bath) and thus can be directly connected to the USB 6008.

Is this possible? I know that thermocouples will not work due to inaccuracies in USB 6008, but what do you think about a PT 100/1000?

Thanks for your help!

Message Edited by rockarmatte on 05-31-2010 08:46 AM

[Henrik_Volkers]

Pt100/100 are fine but need a precise exitation (current source) that is not provided by the 6008, however there are (B5) signal conditioner for industrial use that provide a 10V output (for industrial prices 😉 )

If your temperature is below 120°C a 10mV/K Chipsensor is possible , LM35 or MAX6607/8 to name two of many  or search the forum for digital readout (I2C)  temp sensors.

[rockarmatte]

Thank you Henrik for your tips and advice! I'm very grateful! 

As it looks now, I will examine one of your suggestions: 

The temperature sensor TO-220 (LM35D) - This sensor is analog and its output voltage is linearly proportional to the Celsius temperature. Since the scale factor is 10.0 mV/ degree C. this should work with my USB 6008.

I will start with the TO-220 sensor and get back to you all with the results from the test!

Thanks!

[rockarmatte]

Hi, at this moment I have purchased two sensors:

1) LM35DZ (tempsensor TO92)
2) LM35CZ (tempsensor TO92)

I have tried with the first one (LM35DZ) but I doesn't work properly. There may be several reasons for this:

a) My connections are wrong

b) My programing are wrong

c) The sensor is broken

In order to eliminate a) and b) I was hoping for some help!

Regarding a): I have attached some photos in a PDF document to explain my connections. Are they correct?

Regarding b): I have attached the VI-file. I think I'm doing the right thing but I'm not 100% sure -->

The temperature range for LM35DZ is 0 degree C to 100 degree C. As the input is +5V the relationship between temperature and voltage should be:

Temperature [degree C.] = 20 * Volt       (is this really correct?)

 Although in the manual you can read: "Linear + 10.0 mV/degree C. scale factor".. (what does this mean?)

Please help me troubleshooting

Best Regards

/Mattias

Message Edited by rockarmatte on 06-08-2010 05:56 AM

[rockarmatte]

Anyone? Please.

[ToddH]

It's really unfortunate that no one is able to help you. I am very interested in this issue and would like to know how your results turned out?

[rockarmatte]

I will try to solve the problem by himself and will come back with pictures and a detailed description if I succeed.

[Tom__Sedlack]

So what is not working with your circuit/programming? 

It's hard to tell from your picture but I would assume the leads of the sensor are not all shorted together.  Have you tried reading the sensor using the 6008 test panel to help determine if it's your software or hardware that is at fault?  You should be reading the sensor voltage in RSE mode (voltage referenced against ground).  Make sure the test panel is configured that way as well as your VI.  If you use differential mode, you would need to tie the reference terminal to ground.

Tom