The Many Types of Programmable Timers
The Programmable Timer is used for measurement, display and control in applications that have variables. A Programmable Timer can also work with a single input or, in some cases, a pair of signals. Timers exist because many processes are based upon timed events. Programmable timers are usually electronic and use digital displays, precise digital set-ability, high accuracy, and fast reset times. Digital electronic timers use LCD or LED displays and offer long time ranges and come in a several types.
Preset CountersPreset counters, or predetermining counters, are essentially totalizers that can control an external circuit when it's counted total matches user-entered preset limits. While one or two presets are typical, some models include up to 50 presets. These programmable counters are used in manufacturing and process applications to control batch lot size, material cut-lengths, punching or drilling, stacking, and many other count, position, or length related operations. The programmable version of the preset counter offers maximum flexibility through user selected advanced features such as: input calibrators, movable decimal point, bi-directional counting modes, and output logic options. In some applications, programmable counters may replace two or more individual counters - providing cost effective, customized solutions to your counting and controlling challenges.
When specifying this specific type of programmable timer, consider the following:
- Input - what will be counted and where will the input be obtained
- Count Speed
- Number of digits - based on maximum count value
- Type and Size of Display
- Packaging - requirements and enclosure size
Rate Indicators and ControllersThe second group of Programmable Timers includes rate indicator and controller. Rate indicators provide a digital display of a process. Simple versions connect to a sensor and give a direct readout of frequency or voltage, which represents rate or speed. Units can show variable such as motor revolutions per minute or material feet per minute. Some rate meters have calibration that scales, or converts, the input signal to engineering units using a sensor. Rate controllers add the ability to compare input to one or more values or "alarms". These "alarm" can trigger control outputs or relays to prevent out-of-tolerance operation or take corrective action to bring the process within normal limits. Some programmable rate metering products can measure process times. This is a measurement made of how long a process takes, rather than how fast it is going. They may be used on conveyor lines to indicate the time a product spends in a galvanizing tank or baking oven.
Additional considerations when specifying this particular type of programmable timer, include:
- Ambient Light
- Warning Light/Alarm Requirements
- Additional Power Supply for Sensing Devices/Alarms
- Communication Links
Time Indicators and Preset TimersPreset timers are the third group of Programmable Timers. They are various operating functions that enable the device to activate/deactivate control outputs based upon a preset time interval. The time indicator version displays an elapsed time and is available to register seconds, minutes or hours. These indicators are used for measurement of equipment running and cycling times, product testing and time studies. Many of these timers are used for the automatic control of machine cycles, event sequencing, malfunction detection, and process time regulation. These programmable timers can be in one of three states: rest, timing, and timed-out. When the programmable timer has been reset, the timer does not perform any timing function. The timing period starts when an external signal is received. The timed-out state is the period between the end of timing and when the programmable timer returns to the rest state.
When specifying these programmable timers for your application, consider:
- Control Function - reset, repeat cycle
- Time Range
- Mounting Types
- Service Voltage and Frequency
- Setting Accuracy
- Repeat Accuracy
- Front Panel
- Load - What device will be controlled by the timer and specs
- Cycle Rate
- Action on Power Failure
- Operator Restraints
- Special Requirements - NEMA, high temp/humidity, corrosive, electrical interference
- Agency Approval
Time Indicators, like the Veeder Root 7795 Series above, can be found with many different timing ranges, depending on the application in which it is needed.
Multifunction Indicators/ControllersThe final type of Programmable Timer is the multifunction indicator/controllers. The multifunction instruments are combinations of totalizers, predetermining counter, and rate measurement techniques. They do the job of several instruments, saving time, money and panel space. These devices are used when applications require multi-step, sequential operations by count and/or time. One example is for this device is for liquid transfer and dispensing operations - providing totals and rate functions. The counters described need a signal that represents the unit to be counted, which is often available as a voltage pulse or contact closure. When no signal is available, a sensor will be needed.
Programmable Timers are available in ranges as large as 0.01-9999 hours and as precise as 0.05-5 seconds. Choose from a variety of cycle types, delays times and special considerations such as NEMA ratings.
Programmable Timer Video Overview