A Workstation for Sensitive Experiments?

etrgQUARK asks: "I am in charge of infrared spectrometers at our research center. One of the setups is used to measure the orientation of monolayers at the air/water interface, i.e. the signal we have to detect is very weak and noisy. We already have a great setup with quality components and electronics, except for one piece of hardware: the computer hooked up to acquire the data. How important is the computer in noise-sensitive data acquisition? What are your experiences? Do you have any suggestions on a workstation suitable for such tasks or is it a waste of money to use anything but the average computer system? Unfortunately, the software used is Windows-only."

Comments

Data Logging

[thegrassyknowl]

You should look at expensive, custom data logging equipment for aquiring the information you need. When you have that you can shield it properly. The manufacturer's specs will show the sensitivity/noise/etc and you can select one that can actually record your signals with reasonable resolution.

Don't run a PC anywhere near it if it's as sensitive as you say. PC's generate a lot of noise and they'll interfere with practically any sensitive measurements... take for example your TV. The TV isn't particularly sensitive but your PC can create noise on some of the channels.

Just hook the data logger up to a PC after the experiment is complete.

Amplify the signal you're looking for

[hankwang]

The poster is a bit short on the details regarding what s/he considers to be 'good' quality data.

With a 16 bits ADC you might get 14 bits effective resolution at the 10 V input range. The last 2 bits are often mostly noise even if you shortcut the input. Always use differential mode instead of single-ended such that noise from ground loops is eliminated. (It means it does an analog substraction of the signals on two inputs, rather than compare them to the common ground that may be noisy)

If your noise requirements are much higher, then the best thing to do is to amplify the signal you're looking for before it goes into the ADC board. Use lock-in techniques if you can. For example if you're trying to see variations of 0.001 V on top of a 5 V signal, find a way to modulate the 0.001 V signal (e.g.chop the light source at 1000 Hz) and use a lock-in amplifier to measure the oscillating 0.001 V component and amplify it to some value that is easier to send to an ADC.

Re:Isolators and sensor pods

[Deanasc]

Classic case of engineering not listening to customer requests. The question stated that it was for equipment to monitor the air/water interface. Microwaves no matter how weak will impart some measure of rotational and vibrational energy to the water molecules. Thus increasing noise in the already noisy system. The sensors may be microwave proof but the analyte is not.