measure temperature thermocouple usb

[FFCyrille]

Hi,
I am in charge of building a prototype oven to cook some composite parts. I would like to do this using the virtual instruments capacity of Measurement Studio (I have the standard edition v8.1.2) programming in VB.net.

I have looked at a lot of tutorials and documents on your site but am not perfectly clear on some aspects.

I obviously need a temperature sensor and a relay for my heater. For the temperature sensor I was thinking of using a Watlow sensor of type AXJSME00CP (http://sine.ni.com/apps/utf8/nipc.specs?action=view_specs&asid=1306&pid=5437&tier=3). Price is much more a drive than accuracy at this stage. We would be measuring temperatures between 20C and 300C (70F to 570F).

- I am not clear on if I can use only a device such as the NI USB-6525 or if I also need a signal conditionner?

- Can the USB 6525 output to a relay?

- Anyone has a reference for cheap and simple relays?

- I must admit I got a little confused between GPIB, MDAQ and TEDS...

I will keep on searching but any help will be highly appreciated.
Thanks,

Cyrille

[sendia]

Hi Cyrille,

I am pretty sure you cannot use the USB 6525 to measure a MI termocouple sensor and in general, any sensor because this card only has digital lines. You will need a DAQ card for thermocouples like this (signal conditioning embedded):

https://www.ni.com/en-us/shop/model/ni-9211.html

https://www.ni.com/en-us/shop/model/ni-9213.html

A multifunction card with enough accuracy to measure signals from thermocouples without conditioning (they are quite expensive) or a multifunction card with a input conditioning stage (if you are going to measure few channels, a SCC module could be enough).

About the second question, you can use digital lines to switch a relay only if your card can give you enough current to switch the relay (the relay consumption is not too high for the digital card). Many relays work with TTL lines so I must not be a problem, but you must check datasheets of both products.

There are many companies of electronics components. RS is an example and sell online:

http://www.rs-components.com/index.html

I think the best option for you is to call National Instruments and ask for help. It is free and the can answer most of you r doubts. You can find the telephone number in the website:

https://www.ni.com/en/contact-us.html

Regards,

[FFCyrille]

Hi,

Thanks for your comments. I have indeed called NI directly and they were very helpful. They suggested that I use the following:

NI9211 USB for temperature acquisition using a sensor from Watlow

NI9481USB for the switch. What I am not sure of is the power I can plug in the switch. It says the following:

Switching voltage .......................60 VDC max, 250 Vrms max

Switching current (per channel)

One channel ON .................4 A max at 30 VDC,

1 A max at 60 VDC,

4 A max at 250 Vrms

All channels ON..................2 A max at 30 VDC,

1 A max at 60 VDC,

2 A max at 250 Vrms

I will be using all four channels. Does that mean that I could plug my heat cartridge directly from the electrical outlet in the wall (in spain, 230V at 50Hz) or will I have to use a mechanical switch? I am not sure what the difference is between VDC and Vrms is. If I use a mechanical switch, can you recommend good providers?

Another question, it states that the switching race is 1 operation per second. Does that mean I won't be able to operate the switch at more than 1Hz? I suppose that isn't too important for my project but it will be if we use it for other purposes (controling machines) on other projects.

Cheers,

Cyrille 

[sendia]

Hi

Specifications mean, if you want to use all 4 channels, the addition of their 4 currents cannot exceed 2A if you supply equal or less than 30 VDC (Voltage Continuous Current) or 250Vrms (Voltage alternating current, Vrms=Vpeak/(1.4142).

http://en.wikipedia.org/wiki/Voltage

You don't need electromechanical relay because they are already embedded.

About the operation speed, you are right. This card just can operate at 1Hz because electromechanical relay are very slow (page 12, open time and close time are several ms). Other types of relay are faster but cannot use very high voltages. You can compare the relay cards of this datasheet:

http://www.ni.com/pdf/products/us/c_series_do.pdf (look at the relay time in the page 1 table)