temperature logger

[ee_student]

Hi there!

I am assigned to build a temperature data logger that
[1]can measure from 0 up to 350 celsius,
[2]able to accept both J and K thermocouple,
[3]have at least 20 temp sensors channels,
[4]switching between j and k are provided by software control
[5] necessary to provide cold junction compensation

Am thinking of using AD594 for J and 595 for k TC. or is there any amp that can be used for both J and k? and according to data sheet the AD595/594 are desinged to be used from 0 to 50 deg c. does it mean, i cant use it if i would like to measure up to 350 deg c?

thanks!

 

[giftiger_wunsch]

and according to data sheet the AD595/594 are desinged to be used from 0 to 50 deg c. does it mean, i cant use it if i would like to measure up to 350 deg c?

That would seem to be implied, yes.

 

[ee_student]

any suggestion on what op amp to use then? but normally, op amp cant really take up too high temperature rite? i wonder what does those commercialized data logger use to amplify their signal.

 

[giftiger_wunsch]

Sorry, I didn't read your situation properly, I've now realised I don't know enough about your application or the devices to be able to comment on their suitability. If it's a part which doesn't need to be exposed to the temperature you need to measure with the probe, then perhaps it could be kept within its acceptable range simply through careful insulation.

I'm sure others will be more help than I can be.

 

[ee_student]

itz ok. thanks anyway!! =)

does anyone knw how to switch between ad595 and 594 for each channel? thanks!

 

[ericgibbs]

itz ok. thanks anyway!! =)

does anyone knw how to switch between ad595 and 594 for each channel? thanks!

hi ee,
I have already described to you in detail on the chat line, yesterday, how to do that.

Would you like a block diagram.?

 

[ee_student]

The flow of information would be:
32 input channels -> AD594 and 595 -> multiplexer (i thought of using DG407) -> ATMEGA8 (with ADC) -> SD memory

however, i dont really know how the data logger will be able to identify what type of thermocouple is plugged into it and determine whether to send the signal to 595 or 594.

and im wondering do i use a multiplexer /switch for the connection between input channel and AD595 / 594

thank u eric !

 

[ericgibbs]

The flow of information would be:
32 input channels -> AD594 and 595 -> multiplexer (i thought of using DG407) -> ATMEGA8 (with ADC) -> SD memory

however, i dont really know how the data logger will be able to identify what type of thermocouple is plugged into it and determine whether to send the signal to 595 or 594.

and im wondering do i use a multiplexer /switch for the connection between input channel and AD595 / 594

thank u eric !

hi ee.
Looked thru the devices you have posted, they look a good choice.

Each TC will have its own AD595/4 devices, this will enable the adjustment of each TC's span/offset.

The output from each of the AD595/4's will connect to one of the 16 input pins of the DG407.
If you decide on 20 channels, then you need two DG407,s

The output pins of the DG's will go to the MCU adc input pins.
Use an output port on the MCU to address and enable the DG407's.

OK.?