Agilent 34790/RTD

[Perry_S]

Dear Will,

I have checked on the NI website and it shows that the instrument has been tested. I have not yet found out if the communication is at 60 Hz. I do have a question for you though. Can you acquire data with the instrument at that rate with out any computer interface? Did Agilent rate the instrument as being able to communicate at that speed over the bus?

Perry S.

[Will_Crowe]

Perry,

I just tested it there. I set up channels on the front panel interface of the device and ran it directly (NOT through labview_. I noticed a slight shortening of the gap time-gap as it moved between cards (ie, from the first card to the second and then the second to the third) but the rate at which it scrolled through the 20 channels each time was the same. It still took about a second to scroll through the 20 channels for each card suggesting a data rate of about 20 Hz and not 60 Hz as claimed.

No matter what settings I have been able to change, I have never heard the device click through the channels in each card any quicker...it's always about 20 Hz.

Barry

[Will_Crowe]

Perry,

Following my earlier mail, I just set up 20 channels through the front panel of the device, as DC voltages and I noticed that they sampled much faster than the 20 thermocouples. This must be the root of the problem - that thermocouples are much slower to sample on this device than other channel types...although it does not mention this in the manual.

DC voltage channels can be set with the lowest resolution and with Autoranging off (both suggestions made by Agilent engineers to increase speed) but these options are not available when setting up a thermocouple channel. I thought there was a way to configure the channels through labview but this does not seem to be the case. None of the engineers I spoke to seemed to know much about these settings and how you chanage them. Have you heard, through other sources, that thermocouple measurements are likely to be quite a bit slower than, say, voltage measurements with this device?

Will

[Perry_S]

Hi Will,

I have heard that thermocouples have a response time for each type. This response time is due to the material types of the thermocouples  and the way that they are connected. Since the response is not instantaneous the data is not as available to be acquired as fast as other signals. Please take a look at these links to understand the response time of thermocouples.

http://www.w-dhave.inet.co.th/Thermocouple.html

http://www.omega.com/temperature/Z/ThermocoupleResponseTime.html

Regards,

Perry S.