Load cell to PC interface ??

[Markems]

I have just bought an old Froude Hofmann DPX2 water brake dyno. I am wanting to convert it to a load cell (geting rid of the scales and wieghts) and run some software on my computer instead of all the manual calculations. I have found various free software versions on the net most of them want you to buy there interfaces (expensive £1000 or more). Dose anyone know of sensible priced interfaces or a way of getting it all to work.

 

[itsmoked]

Often in your situation I just get out some form of Basic software.

I get an 8 channel opto-22 type board.

Load it up with the required opto relays. Then just play with the Basic to get the relays to work and inputs to be visible on the computer.

Once there, write the code you need to do what you want. If you have a 12-14 year old have them do the code. They usually have a blast as having something mechanical occur via a computer is lots of fun for them/you.

Ran my wash-machine this way for many years.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[richs]

Hiya-

I couldn't find any information on your particular dyno on the internet.

I'm assuming that this is a cost sensitve job. Besides doing the torque conversion, one also has to know the RPM to do the horsepower calculations. So, I would suggest a digital tach of some sort.

In lieu of a load cell, there might be a "digital scale" with a computer interface on it that you can find at a reasonable cost. Maybe ebay or some such?

As an alternative, a spring with a string wrapped around the shaft of a rotary interruptor (like the ones on a computer mouse) with or without suitable gear ratios (or belt/pulley ratios). One end of the string is attached to the moving part of the spring. The other side to a winder or weight that will retract the string and keep tension on the string (not much). Then as the spring is pulled, the string is pulled along with it, rotating the opto interruptor, causing a digital "pulse" to be sent to the computer. After "zeroing" the device, the force applied to the spring can be correlated to the number of pulses sent by the interruptor. You should include a pair of phased interruptors, so one can determine not only the magnitude of the change of force but also the direction.

This is a "low cost" implementation that will take some experimentation on your part of course. This might be adequate for your needs.

For the tach, another photointerruptor might just do the trick. One can program the computer to count the number of revolutions per fixed period of time which, of course, leads to RPM. Alternatively, a small permanent magnet on the shaft, with a coil of wire and suitable amplification could be used in lieu of the photointerruptor.

By having the program deduce the force on the "force measuring device" and determining the RPM, one can easily have the program determine the horsepower.

For a LOT of programming, one could use one of the cheap digital scales with LED displays and demultiplex the segments to get a reading. However, this is quite a complex task and might be fraught with peril. I know of no such device that allows this, one would have to be developed.

I hope that this helps.

Cheers,

Rich S.

 

[BobM3]

Have you checked out the Labview offerings? They can provide conditioners, a/d devices and graphical programming software that would allow you to display or simply record your load cell readings.

 

[itsmoked]

BobM3 I think he was trying to do this without the bend-over prices otherwise it would be The Ticket.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Check out load cells and interfaces at omega.com
respectfully

 

[Pud]

Used to use these old brakes along time ago - much more fun adding weights/turning the load wheel etc than any electronic system!

Used to have electric brakes too - pretty boring.

Watch the water boiling from the brake outlet - priceless!

Cheers

Harry

btw, was at uni with fellow apprentices who worked at Heenan and Froude in Worcester, UK (late 1960's early 1970's). Now long gone (as far as I know)

 

[Markems]

Thanks you all. I am going to look at Labview and A/D cards.
Will let you know how I get on. Looks like I am going to have to learn somthing about electronics and computers!
Mark

 

[Markems]

I have been looking at A/D cards and devices and have found one at a low cost £89. Even the software that comes with it is Muppet proof (must be if I can understand it). Have been told it's fast enough a will do the job. Will someone please give a second opinion.
Mark

A/D converter

http://www.audon.co.uk/labjack.html

Software

http://www.audon.co.uk/daqfactory.html

 

[richs]

Hiya-

Well, I looked at the links that you supplied. IMHO, the daqfactory is overkill for your application.

As to the labjack, although a great looking device, will still require an external instrumentation amplifier to take the millivolt signals from the load cell (actually it's a balanced resistor bridge) and convert it up from the millivolt range to the volt range of the labjack or other A/D inputs.

Insturmentation amplifiers can be bought off the shelf, however, they are not all that cheap either....Sigh.

There are examples of building your own. One such, from a google search is:

http://www.analog.com/UploadedFiles/Associated_Docs/404380967COMPLETE_IN_AMP_GUIDE.pdf

Which is probably an overload of information, but it's a very complete document on the subject.......you have been warned!


I'm sorry to say, that your research is not over at this time and a little more digging will be required.

Since the links you provided are in the U.K., I'm not going to make suggestions from the U.S.

Hope this information helps! Keep us posted on your progress.

Cheers,

Rich S.

 

[grahamlaming]

Hi Markems

If you want a simple, user-friendly converter to take a loadcell and convert it to RS232 or RS485, London Electronics do a nice model, the INT-L

It will power up to 4 loadcells and lets you scale them to engineering units.

You can add output options to it, such as RS232, RS485, 4-20mA etc.

Nice units, designed to be easy and quick to commission.

Many in use worldwide in tough industrial installations

Hope that helps.

 

[RAH1234]

Markems,

Before you make your decision, you may want to think about the following considerations:

Do you just want to view the data coming from the load cell or do you want to save data to a file? Measuring torque at a static speed and load is different than analyzing a torque curve.

Are you looking for a graphical representation or simple text?

Are you the intended user or do you plan on having multiple users? The more people you expect to use the system, the more work will be involved in developing error handling routines, operator interface, etc.

How much resolution do you require? Assuming your load cell has an output of 0 - 10V, a resolution of 12-bits will only be accurate to 2.4mV, while 16-bits will be accurate to about 0.15mV. Depending on the input range of the load cell, a step-size of 2.4 mV may be unacceptable.

If you just want a cheap, dependable DAQ device, you might want to look at something like this:

http://www.measurementcomputing.com...1535&mscssid=5UKT3V5EAPQV9PKBRT6M3DXXB3H332U7

The included software may be enough to do what you want, and if not the API and code samples will help you develop a more complex system.