DAQ Sensors: Nebwbie needs help

[sdvdl]

I've just purchased a USB 6008 for data acquisition and analysis of a robotics platform and need some help to move forward. I'd like to analyze the following:

1) Power use during operation
- Voltage
- Current (amps)
- Power (watts)
NOTE: The robot runs on 30V DC, and the batteries operate in the 10Amp range
on average, but are capable of sourcing ~150+Amps at peak.
2) Temperature
- Drive motors
- Batteries
3) Motor RPM
4) Shock during collisions

My embarrasingly newbie two-part question is, A) where do I purchase/how do I assemble inexpensive sensors to get this info, and B) once I do that, how do I configure the software to work with the sensors?

For power analysis, I believe I'll need a current clamp/Hall Effect sensor. I have found devices such as those from Amploc (http://www.ampsense.com/AMP200.html) that seem to fit the bill, but I have no idea how to interface these to the USB 6008 or then to "scale" them to the correct values in the software.

For temperature, I've found a dizzying variety of RTDs, thermocouples and/or thermistors, but don't know which will work best with the 6008, nor how to set up hardware/software to get them to work correctly.

For RPM, I haven't found much, but for my application either a light-based or magnetic based solution would work. Still, if someone pointed me to a sensor, I wouldn't know how to configure the software to report the data correctly.

For shock, I've been looking at the iMEMS line of accelerometers from Analog Devices
(http://www.analog.com/en/subCat/0,2879,764%255F800%255F0%255F%255F0%255F,00.html)

Again, no idea how to take a part and a spec sheet and get to a valid reading.

Can someone point me in the right direction?

[johnsold]

It sounds like you need to hire an engineer. Fortunately, you do understand some of the problems. But if you do not know how to read a data sheet or how to connect a transducer to the DAQ device, you probably need more help than a forum like this can provide directly. Many NI Alliance members have the kinds of expertise you need. I have some of the expertise but am not currently in a postion to provide the services.

Lynn

[sdvdl]

Wow, so if I understand you correctly, a non-expert who buys a USB 6008 needs to hire an engineer to take a simple current reading? If that's true, I guess I'll be returning this product as soon as I receive it. I also think that NI is really missing a trick with this product, because many serious hobbyists like myself would really be interested in this product if they sold three or four simple sensor accessories and some provided step-by-step documentation on how to install and take readings from them. How hard could this honestly be?

It seems rather odd to me. Isn't NI supposed to be strong in education? Isn't the 6008 targeted at this market? How do students use this gear without engineers? Is it really completely undecipherable without an instructor? Very sad, if true.

BTW, please note that I didn't say I didn't know how to read a spec sheet. What I said was I didn't know how to get from spec sheet to a "correct" data trace. It seems to me there are instances where the software needs to be tuned to the sensor. I haven't a clue how to do that, nor have I crossed any documentation that tries to explain it. But, please don't let this inexperience be confused with stupidity. I'm not too dim, and while I have no formal training, I do know my way around a multimeter. What's more, I'm highly motivated - probably more motivated than most students who end up having to use this product. If someone like me can't figure this out with a little guidance, NI should really be ashamed. "Don't bother buying this product unless you're an EE" doesn't sound like much of a marketing slogan.

[johnsold]

All I was trying to suggest was that This forum is most useful for answering a specific question about a topic (which might be quite complex), but that it seemed like you had so many questions and uncertainties, that it was hard to tell where to start. I am not affiliated with NI in any way although I have used their products for many years.

If you are a motivated student, you can certainly learn all that stuff on your own and this forum can help. Please do not expect all the answers at once.

I suggest starting with one part at a time. Temperature might be a good starting point. As with any measurement, start by defining what you want to measure: Range of temperatures, Accuracy and resolution, How often do readings need to be taken?, Any special conditions, such as non-contact measurement or measurement of moving parts? Alll these things affect the selection of the transducer. We have not yet addressed signal processing, data acquisition, data processing, or display. Since you already have the USB 6008, we may also have to work backwards from that to try to get a working system for you.

Put together a similar specification for the other measurements you want to make: Voltage, current, poewr, rotational velocity, etc.

When you have these specifications, then we can help with the selection of transducers. After the transducers are selected then the signal conditioning design an proceed. Signal conditioning is a term covering everything that needs to be done to connect the transducer output to the DAQ device input so that you get an accurate measurement without damaging ieither the transducer or the DAQ device.

Lynn

[Travis_M.]

I would recommend starting out with setting up the system and using the examples that ship with the 6008 to ensure that everything is configured correctly. Before plugging in your device, install LabVIEW (if you are using LabVIEW with the device), then install the NI-DAQmx Base 1.4 (ships with your 6008). Restart the computer and plug in the device. Let Windows install the device if prompted. Once this is done you can examine a VI that probes all the channels. Select Start->Programs->National Instruments->NI-DAQ Mx Base->Examples->LabVIEW 7.1. A folder of examples will appear with "Static", "Dynamic", and a couple other lib files. Open the lib titled "USB-600x Interactive Control.llb" with LabVIEW. This will bring up a handy way to test the operation of your 6008 (make sure you are checking the AI channels in the proper mode by clicking the RE or Differential tab). Once you are sure your device is working properly open the same examples folder but try out some of the examples in the "dynamic" folder.

A couple things to watch for: the DAQ assistant and MAX will not work with the 6008/9, so use the configuration utility to make sure the device is connected and working. In addition, the DAQ Mx Base channel controls do not populate with eligible devices/channels even though there is a drop-down menu. You will have to type in the device and channel here (such as "Dev1/ai0").

Good luck with getting started with NI-DAQmx Base, and feel free to post with any other questions you have.

Travis M
Applications Engineer
National Instruments