Basic DAQ system information for temperature and force measurements

[Daam93]

Hi all, 

I am a new user on the forum. I am Danilo an engineering student and for the first time I am gonna decide which kind of DAQ system I am gonna use for some measurements in the process that I am studying.

I am quite confuse about all the informations regarding DAQ system that is why I am writing here trying to see if I have understood same basic principles that I have to follow to choose the right DAQ system.

In my case, I am gonna use 8 thermocouples and a dynamometer to measure temperatures and forces in the process. In that case I think that I need a 16 channel DAQ that will allow me to measure all these quantities. Am I right? 

Furthermore, as long as I have understood, I have also to check the sampling rate and to check the sampling considering that I am using several channel in the same time to be sure to acquire data in a satisfying rate for my application.

Let me know if I am on the right direction or if I am not getting the point of the DAQ system that I am looking for.

Thanks in advance,

Danilo

[.imb]

Hi Danilo

There are multiple ways to design your DAQ system to fit your requirements, and each of them has pros and cons. I see two main solutions here :

• As you said, you can use a 16 channels DAQ device, however, thermocouples output very low voltages and you will have to use a thermocouple amplifier in order to get those voltages in the range of a general purpose DAQ device. For the dynamometer, it depends on the sensor but the voltage levels are far easier to work with. The sample rate is then the thing you have to be careful about if your signals are fast. Be careful of multiplexed devices where you have to divide the maximum sample rate by the number of channels you are using.
• Another way is to use a modular approch (like the CompactDAQ platform) where you are free to use dedicated modules for your measurements. There are a few dedicated thermocouple modules (https://www.ni.com/en-us/shop/category/temperature.html?productId=118148) (you can use either one 8 channel module or two 4 channel modules) and again, depending on the specifications of your dynamometer the choice for this one might change. This will allow you to choose better suited modules for each sensor.

The choice will also depend on the budget you have available and/or the hardware you already have.

Thomas

[Henrik_Volkers]

How fast do you need to sample each sensor?

What type (voltage/current/bridge/resistive/??, bandwidth)  of other signal sources ?

For slow measurements (every 1s for temp for example) a multiplexed DAQ would work. BUT if you want to measure more dynamic signals don't use I wouldn't use a single multiplexed device and mix up TC voltages (µV range) and process signals in the 10V range.

I would use one or more DAQ devices for the TCs (slow , multiplex possible) and synchronious sampled multichannel DAQ(s) for the rest.  The C-Series modules 9214 (16 ch TC) and a 9202 or 9215 or ?? for your other sensors.

Get a chassis with one or more  spare slots ... new challenges with new sensors might come.