The common usage of the word ‘Jogging’ in our daily life is for slow running. ‘Jogging’ or ‘inching’ of a motor also implies the same i.e., to have small movements of the driven machine.
In jogging, starting and stopping of a motor is under the direct control of the operator. The primary objective of jogging is generally, to move tools, equipment or processed material into position very slowly.
A typical example of jogging is a small portable crane which is moved in small incremental steps to position certain material on a processing line in an industry.
In jogging operation, motors are expected to run at slow speed. Therefore, the jogging control circuits are designed to prevent accelerating resistors from being cut out from the armature circuit. This means when the JOG-push button is pressed, the accelerating contactors do not pick up and therefore the whole of the accelerating resistance remains in the circuit.
High resistance in the armature circuit limits the speed of the motor to a low value. A simple control circuit that provides for jogging in one direction only has been shown in Fig.
In the above control circuit, when JOG-push button is pressed, the contact A opens while contact B closes.
Contactor M is energised due to closing of contact B and makes the motor run with all the accelerating resistors in the armature circuit (refer Fig).
Due to presence of high resistance in the armature circuit the motor runs at a slow speed.
Accelerating relays and the contactor circuit are not energised during this operation thus making the motor run at slow speed till such time the JOG-push button is held pressed.
When normal operation of motor is required the START-push button is pressed. The control relay CR gets energized and is held through its own contact CR1.
Contactor M also gets energised and is held throughcontact CR2 . Accelerating relays and contactor circuit also gets energised through closing contact CR3.
Accelerating relays and contactors as discussed earlier will cut off the accelerating resistances in the armature circuit step by step and the motor would attain its final speed.