Need to measure deflection of a garage door under wind loading 1

[dfowler]

Can anyone suggest a type of sensor that would be work for an application where we are testing garage doors between pressurized chambers? The delta in pressure on both sides will cause deflection (simulating wind loads) and we must measure that deflection. We want to take readings from at least 5 points on each door arranged in a '+' pattern, or 9 points in an equally spaced 3 row array. The doors tested will vary both in width (from 8' up to 20') and the heights will vary (both 7' and 10') as well so the sensor arrangement needs to be adjustable. Output signals from each would most likely be be sent to a PLC. These sensors do not have to be super accurate (at least 1/16" increments), so small and cheap would work best.

David Fowler

 

[IRstuff]

displacement sensors would seem to be quite applicable here.

They come in all sorts of technologies: lvdt, capacitive, laser, etc.

TTFN

 

[AFab]

If you want a cheap solution you could attach a leaver or a small rack and pinion to a potentiometer. Apply 10VDC and input the signal into a 0-10v analog input card on your PLC.

 

[dfowler]

I do want cheap, but the equipment probably will need some outside certification (UBC, IBC, UL, etc.) so sensor calibration will be an issue. That is one reason that I am reluctant to devise our own measurement equipment. This also needs to be accurate to at least 1/16th of an inch.
Does anyone have any experience with string potentiometers or string encoders? These seem like lightweight devices that can be readily moved anywhere within my chamber. Are they easily calibrated and reliable?

Davey

 

[AFab]

Encoders are more accurate. Calibration would have to be done using the PLC scaling function. The best way I belive
would be to use a dial indicator to accuratly measure the deflection and then ajust the scaling in the PLC to read the same as the dial.

 

[djs]

Hello;
Check out Linear Displacement Transducer Voltage (LDTV). these units provide a linear volyage with respect to the displacement of the actuator. Check out

http://www.omega.com

 

[cpretty]

Try these guys. Cheap doesn't appear to be an option, but accuracy seems to be excellent.

http://www.spaceagecontrol.com/s054b.htm

 

[dfowler]

Thanks but I am nervous about using LDTV style sensors because they can be much more easily damaged than can other types of displacement sensors, at least in my application. I think the deflection on my garage door will be gradual at first and then will catastrophically fail and bend inwards at least several inches - probably quickly and violently. Also my surface will not remain perpendicular to the sensor, rather it will be an increasingly bowed surface during the test. I do like the string encoders and am leaning towards using them in my system.

Davey