Motor Amerage to 4-20ma

rodney312s

Member
R
Join Date
Oct 2005
Location
Kansas
Posts
34
I am currently using a compuwatt on an elevator motor to tell how full the elevator is and i am having some trouble with it. I think the compuwatt is alot more than what i actually need. Does anyone have any suggestions for a product similar to a current transformer that will produce a 4-20 signal to a plc that is simple and effective to use??
 
Hua??

Rodney, is this a conveyer or a "people" elevator?

If it's an elevator, (the type that goes vertically from floor to floor), you measure the load when the elevator is static. This would be done with a load cell on the hitch plate or a strain guage device on the crosshead.

If it's a continious conveyer then you'd measure the load by current draw.
 
elevmike said:
Rodney, is this a conveyer or a "people" elevator?

If it's an elevator, (the type that goes vertically from floor to floor), you measure the load when the elevator is static. This would be done with a load cell on the hitch plate or a strain guage device on the crosshead.

If it's a continious conveyer then you'd measure the load by current draw.
Click to expand...

Good point Mike.

That leads me to a question however? Shouldn't you nevertheless be monitoring the load on the motor? Is it necessary to know that the motor is nearing a trip load so that some sort of action can be taken to avoid trapping people in the elevator? How is this handled in a commercial elevator?
 
Hi Aaron,

In a commercial elevator load weighing takes place when the car is at the floor with the doors open. If the elevator is overloaded the doors wont close and a buzzer sounds to alert and prompt some of the passengers to get off. Additionally if the car is filled to capacity, then it might bypass hall calls until the load-weighing device indicates that there's spare room or capacity in the elevator to make more pickups.

The motor is equipped with overload protection via the Drive or other motor protection devices such as a RPR and Max run timer. It makes no sense to monitor motor load to indicate car weight due to the fact that by the time you get usable feedback, it's too late to do something about it because your already in flight.

It would be kinda like determining if an aircraft is overloaded based on how much power it takes to get off the ground. By the time you've determined that, your plane and passengers are pretty well scattered in the local school yard.

In the case of a continuos inclined conveyer, such as an escalator you would use a motor load device to monitor product or to prevent adding or overloading the conveyer. In this case you really have no other option, and you don’t have a "captured audience", allowing you to prevent overloading by alerting when a near full load condition exists.
 

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