daq and sensors question

[miketv]

Hi, I am working on a semester long project:

build a data acquisition system, with the following sensors:

RPM
Torque
Strain of material
Temperature
Noise
Vibration

I am starting from scratch. I have experience in digital design, some embedded system stuff, and the usual - C/C++.

I don't have much experience in DAQs and have no idea whats out there and how to start on it. I have a limited budget of lets say 250$. The system needs to be portable as well, as it will be put on a moving object. I do have access to Labview through school.

What I am looking for is some pointers and help on getting started, info about sensors, about DAQs, and all that. So any info is much appreciated. I'm not even sure if I'm posting in the right forum.

thank you

-Mike T,

[preston_johnson]

Can you tell us what the unit under test is?  The RPM sensor may be a once per revolution pulse.

PCB, www.pcb.com, has some nice vibration sensors

Thermocouples are inexpensive, and strain sensors may be a bit more expensive.

For portable, you may be interested in USB DAQ devices.  We have several that will work with LabVIEW

Which University are you at?  There are some advance signal processing libraries that might be available to you for analyzing and displaying the data.

Is there a traditional instrument that has been used in the past?

[miketv]

I am a Computer Engineering senior at Virginia Tech. I am working on a senior design team, with 5 other Mechanical Engineers. The project is a prototype CVT (Continously Variable Transmission), the size of a 10inch diameter sphere. My role on the team is to build a data acquisition system for it. For example, the RPM sensor will detect how fast some of the internals of the transmission spin. In the past, on another project, simple strain gauge was used, which was hooked up to a voltmeter, that recorded the max. The CVT will be tested on a bicycle first, so it the data acquisition system needs to be portable

-ddanj

Message Edited by miketv on 01-25-2006 10:50 AM

[preston_johnson]

You can choose from the NI low cost USB devices at:

https://www.ni.com/en-us/shop/category/multifunction-io.html?page=1&productId=118688&BusTypeFormFact...

[miketv]

What kind of sensors would be compatible with it? I see the input range is kinda limited 1-20V, which means I'd have to amplify the sensor signals probably?

thanks again

-ddanj

[Laura F.]

Hello miketv,

I think you may be confused about the input range.  The specification is that the input range is +/-1V to +/-20 V.   You can choose the range in software that works best for your signal.  You then get the resolution of that device over that range.  For example, if you chose your range to be -1V to +1V on a USB-6009 which has 14 bits of resolution, then the voltage resolution you would see is

Range/(gain*2^bits) = 2V/2^14 = 0.1 mV. 

So, you have to check what signal levels you will get out of your sensors to determine if you will need to amplify the signals or not. 

Hope this helps,

Laura

[miketv]

Thanks for the clarification Laura.

I checked out PCB.com, and called them - the sensors they sell are super expensive - rotary torque sensor is $3600. I'm looking to spend the least that i can, since this is just a school project. Any other suggestions for places that sell less expensive sensors? I'm not sure what would even be compatible with that 6009 unit.

thanks

[Laura F.]

Hi Mike,

I am not too familiar with the best places to purchase sensors but others in the forum may be.  A quick Google search for rotary torque sensor had a lot of hits.  Since you are doing a school project, are there labs around that you can borrow sensors from?  It seems that your project has quite a few sensors involved, can you reduce the number that you need so you don't have to purchase as many?

Sorry I can't be of more help,

Laura

Message Edited by Laura F. on 01-27-2006 04:59 PM

[E Murphy]

Hi MikeTV:

Try ctconline.com for accelerometers. They have piezoelectric units for less than $70. You will need a cable (maybe you can assembly it yourself) and a power supply (limited current, 2 to 4 mA) this you can also build it. You will require a special diode (Motorola)

For the torque sensor, you can suspend the motor around it´s shaft and use  an arm and a pressure sensor to counteract the torque. The pressure sensor costs about $10 (Motorola) and you can select it to cover a specific pressure range.

For temperature, you can buy transistor like sensors from National Semiconductor, with 10mV/degree C for about 1.5 or $2 each (try Radio Schack) they are good up to 100 C.

Regards

Eduardo Murphy