Hoping for some guidance: application is a vertical crane and I need to determine the velocity 'safely'. I'm thinking an air velocity sensor system or a surface speed sensor with Ethernet so it can be monitored wirelessly to prove speed calculations.

Resolution is not too important.. like +/- 1 foot/second and the terminal speed is somewhat slow at 20 ft/sec..

Has anyone had any experience with this type of sensing problem?? It can't be hand-held because it is checking a speed safety device - kinda like an elevator!!

Thanks in advance

Cheers from:
Jeremy Pollard, CET The Caring Canuckian!
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You haven't said what distance you are operating over, or if there is more than one axis moving. However, you might want to consider using a string pot. I have heard of them with up to about 30 to 40m of stroke. If you connect one to a chart recorder you will get the complete motion profile versus time, not just the instantaneous velocity.

 

Jeremy... how about:

1) An optical-tach to monitor a rotating element in the drive train.

2) Then have the optical-tach output trigger a spark plug.

3) Finally use a commercially available wireless-tach, used to monitor combustion engines, to transmit to a receiver.

Or

4) Use the optical tach to drive an auto-tire pressure unit.

Regards, Phil Corso

 

Thx Phil..

there isn't a rotating 'part' exposed that can be used. There is a vertical rail that could be used and as such a tach that measures surface speed SHOULD work, but I have not encountered an application where the sensor is the component moving.

I am in an area of quandary

Cheers from :
Jeremy Pollard, CET The Caring Canuckian!
www[.]tsuonline[.]com
Control Design www[.]controldesignmag[.]com
Manufacturing Automation www[.]automationmag[.]com
3 Red Pine Court, RR# 2 Shanty Bay, Ontario L0L 2L0
705.739.7155 (Cell # 705.725.3579)

 

Sorry Michael ..


I always forget something we are working with a height of 120 feet. If I could find a radar gun that is accurate enuff that that would work, but they are in MPH typically and too granular.

We have an absolute encoder on the drive wheel, and we are trying to confirm the calibration of the PLC code using the encoder, so that the velocity can be relied on for safety testing.

Max speed is around 1 m/s - will check the string pot hadn't even heard of that technology - thx

Cheers from :
Jeremy Pollard, CET The Caring Canuckian!
www[.]tsuonline[.]com
Control Design www[.]controldesignmag[.]com
Manufacturing Automation www[.]automationmag[.]com
3 Red Pine Court, RR# 2 Shanty Bay, Ontario L0L 2L0
705.739.7155 (Cell # 705.725.3579)

 

Jeremy... how about another:

5) Mag pickup via a Hall-switch.

Regards, Phil Corso

 

120ft is approximately 37m. Put "string pot" into Google and you will come up with half a dozen or so options on the first page that will work in that range (50m seems to be common). String pots are also known as "cable pull sensors" or "wire pull sensors". They have a wire wrapped around a spring loaded drum. The wire can be anywhere from a few centimeters to tens of meters long. When you pull the wire out the drum rotates which in turn rotates a geared potentiometer or encoder. They typically have outputs with 0-10v, 4-20ma, or serial or some sort of industrial network. The 0-10v output would probably be the easiest to work with for an ad-hoc installation.

I'm assuming you could attach the string pot body to the ground at the bottom of the elevator and then attach the cable to the cab, car, bucket, or whatever the moving element is. If you use (rent) a multi-channel strip chart recorder, you can plot position versus time and also add in other signals such as the motor start/stop, PLC outputs, etc. You might also look at whether an inexpensive USB data acquisition box could do the job instead of an actual chart recorder.

If you get the right sort of chart recorder you can download the data to your PC (a data acquisition box brings the data in directly of course). You could then manipulate it in a spreadsheet to calculate position, speed, acceleration, stopping time, reaction time to other signals, and anything else you want.

If you are just calibrating the speed though, why can't you just do a timed run over a measured distance? I am assuming that at 1m/sec you are reaching full speed fairly quickly. After that you just need a timer (e.g. Omron panel mount style) and two sensors (start and stop) a measured distance apart.

 

Thx Michael and Phil... will check out the string pot... due to the application limitations, the speed feedback has to be real time.. so the time/distance thing wouldn't work - probably forgot to mention that too

Thx guys - appreciated

Cheers from :
Jeremy Pollard, CET The Caring Canuckian!
www[.]tsuonline[.]com
Control Design www[.]controldesignmag[.]com
Manufacturing Automation www[.]automationmag[.]com
3 Red Pine Court, RR# 2 Shanty Bay, Ontario L0L 2L0
705.739.7155 (Cell # 705.725.3579)

 

Jeremy... Any possibility of sending a sketch or photo of your installation?

Phil

 

Will be tough Phil the app is an ASRS crane rising 140 feet into the air and is 40 years old. A tubular frame exists.. the carriage runs up and down on chains.

The install is not a permanent install just there to prove calibration(s) .. still not sure what to do but I am leaning towards air velocity sensor(s)

Wierd app since the vibration may knock the crap out of a sensor

Cheers from :
Jeremy Pollard, CET The Caring Canuckian!
www[.]tsuonline[.]com
Control Design www[.]controldesignmag[.]com
Manufacturing Automation www[.]automationmag[.]com
3 Red Pine Court, RR# 2 Shanty Bay, Ontario L0L 2L0
705.739.7155 (Cell # 705.725.3579)

 

Jeremy... if a chain is used, then there must be a sprocket. The sprocket has teeth! Are the number of teeth in one revolution proportional to distance traveled?

Phil

 

True enuff Phil.. But not accessible.. I think I will go with a Bluetooth air velocity meter/sensor.. at least see where it takes me

Will report on its suitability.. the actual hardware (application ie crane) is the limiting factor as well as the temporary wireless requirement

Thx for all of your input all

Cheers from :
Jeremy Pollard, CET The Caring Canuckian!
www[.]tsuonline[.]com
Control Design www[.]controldesignmag[.]com
Manufacturing Automation www[.]automationmag[.]com
3 Red Pine Court, RR# 2 Shanty Bay, Ontario L0L 2L0
705.739.7155 (Cell # 705.725.3579)

 

Jeremy... Did you solve the problem?

Regards, Phil