NI USB-6008

[ubongakpabio]

Hi, am using a USB-6008, which has 8 analog input channels and can be used to acquire data from 8 thermocople maximum,Assuming that this system is the prototype for a 100 channel temperature logging system, specify a hardware configuration which would enable this task to be performed efficiently. what is the available systems for signal conditioning and acquisition and what is the cost estimate

[johnsold]

People on this Forum generally will not specify a system for you.

1. The USB-6008 alone is not well suited for thermocouple measurements because the resolution is too low and it does not offer cold junction compensation.

2. Contact your NI sales representative. It is their job to help you specify the appropriate equipment to make a measurement system.

3. Consider a commercial temperature logging instrument which has the signal conditioning and A/D conversion built in. Find one which can communicate with the computer via RS-232, Ethernet, or GPIB.

Lynn

[ubongakpabio]

i used an AD595 thermocouple amplifier, to provide me with signal conditioning and cold junction compensation, is it therefore possible to configure this prototype to achieve 100 channels, may be by multiplexing or something

[johnsold]

Yes, that could work. The AD595 is a well-regarded device. I am actually working on a project using AD594s and USB-6009 right now.

You could use 9 CD4051 analog multiplexers, the digital output port of the USB-6008, and a few other logic ICs to make a multiplexer to handle 100 channels.  It would take a little effort to do a design and to check the amount of error introduced by the switching but I think it should be quite feasible, especially as a prototype.  If you have the capability to build the circuits, this could be a relatively inexpensive solution.

Lynn

[crossrulz]

Personally, I would just get a cDAQ chassis and 7 of the 9213 (16 channel thermocouple module).  No need for external circuitry or anything.  Just set up your DAQmx task in tell it to read.

[ubongakpabio]

thank you very much, in getting 7 USB-9213

NI 9213
Module Only - 780493-01	Qty		£ 915 each £ 823.50 each

, would i also need, 7 AD 595 thermocouple amplifier. is there any other optional accesories i need to carry out this task. how do you see the USB-6225 that has 80 channels. i am a student trying to my project, and cost is a very important factor. my project objective is to cature a 100 channel of signals from a type k thermocouple.

779973-06

NI USB-6225 M Series Screw Term U.K. (240V)

12 - 20

£ 1,520.00 £ 1,368.00

[ubongakpabio]

please can you be a bit more explicit on the logic IC's that i need.

and in the case of the design, does it entail i would require 9 AD 595 thermocouple amplifier since am using 9 CD 4051 analog mulitplexer. thanks so much

[johnsold]

I do not have the time right now to do a complete design. The idea is that three of the digital lines would go to the address lines of the CD4051s. I just checked. The USB-6008 had 12 DIO lines so the other nine lines could be used for the Inhibit inputs of the CD4051.  No extra logic required. You would need to check the start up state to make sure that multiple AD595s are not shorted together between the time power is applied and the software configures the digital port and writes initial data to the port.

I was thinking of multiplexing the outputs of the AD595s.  To multiplex the thermocouples directly requires great care in managing errors. Typical leakage currents on the CD4051 are in the pA range and probably would not be a problem. Worst case leakage can be 200 nA and that likely would introduce errors. What is the range of temperatures you will be measuring? Do you expect to have power line frequency interference or other large signals which could get into the system?

Lynn

[ubongakpabio]

am measuring the room temperature between 20 to 30 degree celsius. the interference i may have is from the mains pick up. here is the design method i was thinking of. since USB-6008 has 8 analog inputs, and am to acquire signals for 100 chanels, i would then use 13 analog CD 4051 multiplexer, meanining 8 thermocouples to one, giving me a total of 104 channels, and i would also use 13 AD595 thermocouple amplifier to condition the signal output from the mulitplexer before it enters the DAQ device.

But from your last post, I here you talk about using the Digital Inputs of the DAQ. Is that possible in this case? Earlier you advised I could use 7-NI 9123, to obtain 100 channels, I had computed the cost and it was about 6000 pounds.how do you see SCXI-1175 and PXI 2575, which is less expensive and can also be used to acquire 100 channels.

[Dennis_Knutson]

You say you would use 13 muxes but you only have 8 inputs to the 6008. I don't see where you have enough analog inputs or digital control lines. For a reasonably priced solution, you might want to think about scaling back on the number of channels. Personally, I would use an ad595 per channel.