# How to compare multiple data acquisition systems?

For an application of displacement measurement under 1 kHz, I have 3 options to choose from. The application is automotive. Unfortunately I don't have deep electronics knowledge and the catalogues contain so many abbreviated expressions in the names of their connectors, etc.

What table of comparison in parameters would you suggest to classify them as best and to also justify them with my needs in this frequency range?

• The temperature range is up to 1000°C.
• The movement range is ±50mm
• Frequency : automotive range but let's say 1 kHz.. bolting can be the solution due to the temperatures.

I also have seen a table like this, but I would like to widen it to more parameters :

• Can you give more information on your requirements? What is max displacement you want to measure? What precision? What temperature range? Do you need noncontact or can you bolt / glue the transducer to the part? Oct 26, 2019 at 13:54
• @DanielKiracofe I added some details to the question as per your reuqest Oct 26, 2019 at 13:57
• Wow, 1000 C is pretty steamy. Wouldn't have expected that high for automotive. Did you mean 100 C? Also, 1 kHz is the max frequency you want, but what is the minimum frequency? That will matter if you go with a piezo electric accelerometer for the transducer (probably your only option at 1000 C). Also you said the max range is 50 mm, but what's your min resolution you care about? 1 mm? 0.1 mm? 0.01? i.e. if the true value is 12.345 mm, do you care if you get 12.3, or do you need all the digits? Sorry for so many questions, but your question is very broad and need to narrow it down. Oct 26, 2019 at 19:18
• Sure ! thank you for the questions, I widened the rangees actually, the temperature would not really rise to 1000, it will be 300-500 for the sensors. but I am caring about the DAQ. 1kHz is also too high, it's max 300Hz. and I am not sure about the precision , but maybe something between 0.1 and 0.01 mm Oct 26, 2019 at 19:50
• let me try to rephrase. the data acquisition system reads voltage. So you need to know what is the minimum and maximum voltage that you need to read. That's going to tell you what data acquisition system you need. Where does the voltage come from? the transducer. So you need to figure out the full specs of the sensor first, then you can select the DAQ. Do you have a sensor already picked out? If so, we need the details. Oct 26, 2019 at 21:21

Edited based on new information provided

The most important thing to start with is: what resolution DAQ do you need? 16 bit is fairly standard, cheaper ones will be 12 or 14 bit. more expensive ones will be 20 or 24 bit.

Based on the specs you provided, Firstmark series 173-176, the conversion is 165 mm = supply voltage. Max supply voltage is 35VDC, but you could use anything. You didn't provide the min frequency you are interested, so let's just assume you need all the way down to 0 Hz, i.e. needs to be DC coupled. Most basic DAQ systems would be able to read -10V to 10V. You could get something that would read up 35V, you'll need something more expensive and complicated, so just assume you are keeping it simple and use 10V supply voltage.

A 16 bit ADC would set +32768 = 10V, and -32767 = -10V (note 2^16=65536, and we are using half that range for positive voltages and half for negative, hence 65536/2=32768... note that as I'm assuming DC coupled above, half the voltage range is unused... i.e. the DAQ system is setup to use -10 to +10, but you'll only be using 0 to 10V. If you can assume AC coupled you can use the whole range, but in that case the minimum frequency you can read would be a few hertz, won't get DC). So the smallest voltage you could read is 0.0003V.

With the assumption that 10V=165mm, this means the smallest displacement you could read is 0.005 mm. That would appear to meet your specifications. So a 16 bit DAQ should meet your needs, you don't need to spring for anything more expensive than that. On the other hand, a lot of cheaper systems might be 12 bit. Those will be 16 times worse resolution, i.e. minimum value you could read would be 0.08 mm. Probably would not work for you.

you were also asking about "40 kS/s", that's 40,000 Samples/second. That is not the maximum frequency that you can record however. General rule of thumb would be divide sample rate by 2.5 to get the maximum frequency you can record, which is called the "bandwidth". In this case 40k/2.5 = 16 kHz. You are referencing 7.2 kHz in the comments, which is less that I would have expected for a 40k sample rate. But since you said that you only care about signals at 300 Hz or maybe 1kHz anyway, this will be plenty for you.

while I'm thinking about it, another thing you should be looking at is whether the DAQ has built in anti-aliasing filters. Virtually all of the good ones do, but some cheaper ones do not. Unless you are 100% sure you know what you are doing, make sure you get one with an anti-aliasing filter.

I'll also say that most of the big DAQ manufacturers have pretty helpful sales engineers. Just call the company up and tell them what you are trying to do. They can probably point you in the right direction.

• Thank you so much for your amazing response. Ok I had to share the sensor model, it's a wire position transducer. Firstmark, series 173-176 Oct 27, 2019 at 21:24
• Strangely, on the daq data sheet, there's no data on the bits : 40kS/s :what is it? And 7.2 kHz signal bandwidth. Oct 27, 2019 at 21:26
• Please don't remove your old answer due to the sensor. Just please add to that. I need to ask : where does the 37268 come from? And how did you get to 0.0003V? Oct 27, 2019 at 21:35
• 37268 was a typo. I meant 32768=2^15. I updated the answer with the new information you provided. Oct 28, 2019 at 2:00
• I dunno if some DAQs use some other number representation, but a 16-bit 2's complement number ranges from -32768 to +32767, not -32767 to +32768. (Of course this is unlikely to affect OP's choice of DAQ system) Oct 28, 2019 at 4:44