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Last Post 06/07/2013 8:44 AM by  Larry Laster
Monitor AC motor Currents on Conveyor
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Larry Laster
New Member
New Member
Posts:2


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06/06/2013 1:56 PM
    I would like to know the best product available. What we are trying to do is monitor current on a conveyor that has a history of breakage. The idea is to monitor the current of the AC motor into the PLC analog card(0-10)vdc and then stop the conveyor before major damage. The motor is 460 3 phase 15 horsepower 17.22 amps. When starting the conveyor the current rises to 80 amps and once the conveyor is moving the current draw is around 6 amps. We are looking at your model CR4211. Does this require a load resistor or can it be wired directly into the Analog card(0-10)vdc. We are thinking to use the 0-20 amp range to keep the ratio at a lower level. How much over current will the CR4211 accept and what length of time.
    Tony Hodges
    CRM Staff
    Basic Member
    Basic Member
    Posts:154


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    06/06/2013 4:20 PM
    Dear Sir,

    The CR4210/11 series will be able to measure this current and output the voltage, please note that over current on the CR4210/11 will cause over voltage at the output as it is a self powered unit with no regulated power supply.

    Additionally you also might find that the response time of the transducers is inadequate for interrupting the conveyor operation. Typically large motors will generate damaging torque long before the response time of 250 mS for the transducer plus whatever time it takes for the PLC card to read and activate a limit.

    Typically, emergency current overload switches of this nature are stand alone and are applied directly to the power of the motor, and the PLC and computer systems simply monitor status. The delay time is the reason for this typical setup.

    We have a product, a CR4395 current sensing relay which can be used in this fashion. It has a set point, which when exceeded, will trip a relay that can be used to interrupt the power within the motor. It is available in various time delays to guarantee inrush does not trip it, but fast enough to guarantee safe shutdown. I have attached the catalog page for the CR4395 AC Current Sensing Relay.

    Please let us know if you have any other questions.
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    Larry Laster
    New Member
    New Member
    Posts:2


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    06/07/2013 8:44 AM
    Thanks for the feedback. We have used an item simular to the CR4395 called the Load Sentitial. The problem is with nuisance trip out unless the time delay or the current settings were turned up that they were ineffective. By monitoring the current in the PLC we will also be able to track when scrap is being jammed up under the conveyor on a daily basis. We are aware of the time delay however this is a very slow conveyor with a large gear ratio.
    Thanks
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