If the gravity take-up is designed properly with the correct counterweight based on sag and drive slippage why would you need a tension switch? A gravity take-up provides automatic tension.

If it starts slipping add more weight and someone calculated the weight wrong. It is not hard to calculate the weight req'd. ■

Roland has touched on a good point. If your client insists on some sort of tension monitoring device to prevent slippage there is a way you can do it.

Install a zero speed switch on a non drive pulley. We put a target around the pulley drum or screwed into the end of the pulley shaft that covers 50% of a single rotation. Then we install a proxy switch to pick up that target as it rotates. This signal from the proxy is fed to our PLC then the PLC monitors what is normal or abnormal by counting the pulses. Each pulse on and off is equal to one revolution. We then program set points that the PLC knows is not normal and shuts down the system and alarms a zero speed alarm. You may wants this to just alarm and not shut down (customer's choice on that one).

This type of system must also include a by-pass tiimer during start up.

If the system does not have a PLC then you could go with a unit such as a Milltronics Motion Sensor. See attached.

Hope that helps.

Attachments

7400-291 (PDF)

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It's not a question of detecting belt tension, but of detecting belt tensions. This is because wether the bet slips on the drive pulley depend on T1 and T2.

For practical purposes with a gravity tensioning system we know the value of T2 (providing the takeup is free to move).

By using a torque measuring coupling between the drive unit and the head pulley we know Te ( = T1 - T2 ) and using T2 can establish T1.

All that's necessary is to monitor the ratio of T1/T2 and set off a warning if the ratio approaches the value where the belt slip may occur.

Simples ■

We have provided several belt slip systems by supplying 2 magnetically coupled pulsing sensors to the shafts of the head and tail pulley. A comparative ratio is learned by the PLC, which alarms when it senses a change in the ratio. ■

Originally Posted by dlott

My customer is asking me to supply a "tension switch" that will detect " conveyor belt being looser than it is supposed to be and will soon start slipping". The conveyor is approximately 290' long w/78' of lift and a 40hp shaft mounted drive. It is supplied w/a gravity take-up. Has anyone supplied anything like this before?

Gary and Roland are both right on this and

apparently you do not have enough weight

in the weight box apparently.

What bothers is we dont know if the belt is

being overloaded and if your client is overloading it and

mentioning same.

And if the belt does not have an all weather cover

it may be wet as well and have issues with traction on the

bottom ply.

You have almost 600 feet of belt not including the

take up travel length.

You have 700 over foot of belting in the flight so

cuttiing a bit out annually will not hurt things as the

belt stretches.

What is the total length of the upper and lower

belt strand at work under way with loading

and no load including the gravity take up travel length?

Is the take up:

Tower mounted with a guided vertical basket counterweight

or a tracked sled?

Are the snubber pulleys lagged or not?

Is the tail pulley a beater/cleaner pulley or a smooth pulley?

My other question is this;

Have you ever taken any belt out of the belt

flight and respliced it at any time?

It sounds as if you have not removed

any belt at all.

I think that is huge part of the problem you have.

Dont forget that the weight sled will bounce

at start up and will eventually settle at its equilibrium

during the load/no load conditions at start up

I would remove at least 2 meters and resplice it

before you did anything else.

lzaharis

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dlott hasn't responded to any of the points raised in this thread, why

lzaharis, why does your post have such a large font and so many blank lines at the end of it

The question was that possible slipping was sensed BEFORE slipping occurred. So surely that rules out the normal approach that senses slipping AFTER it occurs by monitoring the rotation of driven and non-driven pulleys. ■

I set the large type size especially because of eye strain when I am tired and as usual I hit enter a 10 or 12 times out of habit, I will try to remember not to do that from know on.

leon ■

Originally Posted by designer

By using a torque measuring coupling between the drive unit and the head pulley we know Te ( = T1 - T2 ) and using T2 can establish T1.

And here's a torque measuring coupling to get us started --

http://www.indmeas.co.uk/FilestoreDo...&title=imltfc ■

for someone that has a concern from his customer doesn't seem too interested in reading our replies.

Here is his last activity:

dlott

Registered User

Last Activity: 7th July 2010 7:34

His only post was made at

7th July 2010, 7:16

It looks like he waited a total of 18 minutes for his reply and moved on. Sorry but the world does not revolve that way. ■

Strange as he filled in all his details sensibly and works for a "Superior" company

Anyway, his question did start me on line of thought that hadn't come to me before ■