Figure 10.1 Counters
Counters are devices that will receive a string of count pulses from a machine operation and perform an output function based on a number of counts predetermined by the user. Most counters, like timers, can have interval and delay operation. Interval operation means that a load will be actuated when the unit is counting. Delay operation means that a load will be actuated at the end of the counting cycle. Solid-state and electromechanical versions are available.
Counters are generally thought of as devices that tabulate or count "things" such as bottles, cans, boxes, castings, and so on. In many industrial control systems, it is necessary to count something that affects a controlled process. When the count reaches a certain number, a control action is initiated. In a mechanical counter, every time the actuating lever is moved over, the counter adds one number, and the actuating lever returns automatically to its original position. Resetting to zero is done by a pushbutton located on the side of the unit. In an electromechanical counter, the count setpoint can be adjusted by the knob on the front of the unit. A progress pointer, indicating the count progression, advances clockwise, from setpoint to zero. A solid-state counter has high speed pulse operation with 100 percent accuracy and has may programmable features. Counter output action occurs when the count total indicated by the thumbwheel switches is reached.
(a) Electromechanical Counter
(b) Mechanical Counter
(c) Solid-State Counter
10.2 Types of Counters used
The circuit of counters operates as follows :
- The sustained control switch is closed to energize clutch and enable the counter to- receive and register counts
- Instantaneous contacts transfer
- Each time the count switch is momentarily closed, a pulse is applied to the cout motor to register a count by moving the count progress pointer toward the zero point on the dial
- When the progress poiter reaches zero, the unit is counted out and the delay switch operates to turn output A ON and output B OFF
- Additional counts will not be registered until the unit is reset
- Opening the control switch to remove power from the clutch resets the counter
Most solid-state counters can count up, count down, or be combined to count up and down. An up-counter will count up or increment by 1 each time the counted event occurs. A down-couter will count down or decrement by 1 each time the the counted event occurs. Normally the down-counter is used in conjuntion with the up-counter to form an up/down-counter equipped with separate count-up and count-down inputs.
Source :
Petruzella, Frank. (1995). Industrial Electronics. Mc Graw Hill.291-293
