Programmable Industrial Timers For Single Or Periodic Events

Using a programmable digital timer for timing and stopwatch

Industrial timers are now available in the form factor of a 1/8 DIN digital panel meter or counter. Designed for permanent installation in an instrument panel, these have now become production tools for repetitive operations. Two timing types are most common: timing of single events in a stopwatch mode, and time interval measurement for the average of repetitive events. In both modes, the start and stop times of events are determined by electrical signals wired to the instrument, as opposed to an operator pressing a button.

In a stopwatch mode, which is the most common, separate signals can be applied to two separate input channels A and B. In A-A Stopwatch Mode, time is measured between a start pulse and a stop pulse both on Channel A from either the positive or negative edges. This mode allows measurement of pulse width. In A-B Stopwatch Mode, time is measured between a start pulse on Channel A (positive or negative edge) and a stop pulse on Channel B (positive or negative edge). This mode allows inputs from different sources. In addition, the A and B inputs can be tied together to start the stopwatch with one polarity and stop it with the other polarity.

In time interval mode, time is measured between inputs on channels A and B. Timing starts when a pulse is applied to Channel A (selectable positive or negative edge), and ends when a pulse is applied to Channel B (selectable positive or negative edge). In case of a single pulsed signal, the A and B inputs can be tied together. A positive or negative slope may be selected to start timing, and the opposite slope must be selected to stop timing.

Both modes offer a high resolution of 0.2 µs, since timing is achieved by counting 5.5 MHz clock pulses. In stopwatch mode, this resolution allows measurement of the speed of a bullet as it traverses a known distance. For long intervals, the display is updated continuously during timing. In time interval mode, multiple integral time intervals are averaged over a gate time which is selectable from 10 ms to 199.99 s and also controls the display update time.

6-digit digital timer display

Time may be displayed H, M or S format with six-digit resolution. The longest single-event timing interval is 999,999 hours. The highest resolution is 0.2 µs. The event time may also be displayed in HH.MM.SS clock format with 1 s resolution. The stopwatch display is updated during timing at a rate controlled by a gate time, up to 25/s. It is reset to zero when the next start pulse occurs. Accumulated time from multiple events is also tracked and may be displayed up to 999,999 hours. A common application of industrial timers is to track cumulative machine use in hours to determine the need for machine maintenance.

Signal conditioner for programmable digital timer

As opposed to a handheld stopwatch, which is only designed for a mechanical input, an industrial programmable timer needs to be designed for a wide range of signal types, which can include milli-volts levels signal from magnetic pickups, flow meter signals, AC power line inputs, CMOS/TTL logic signals, and proximity switches with a PNP or NPN output, and contact closures. This type of flexibility is achieved with FR signal conditioner, which allows different electrical input circuits to be switched in by moving plug-in jumpers.

Features to look for in a programmable digital timer Look for a standard size, such as a 1/8 DIN panel cutout, for easy installation in a control panel. Look for programmable features that will allow the instrument to function in multiple control modes to turn machinery on and off using relays. Look for programmability to add offsets and to time up to a preset or to time down to zero. Look for a dual-channel pulse input signal conditioner for use with different start and stop pulses. Also look for ease of use. In addition to front panel programming, the manufacturer should offer Windows based setup software that runs on a PC that is connected to the instrument.

Look for options that will allow the instrument to work as part of a larger system and to be interfaced via an Ethernet network. A state-of-the-art rate meter should offer a choice of plug-in boards for communications, control, and network use. For example, serial interface boards include Ethernet, USB, RS485 and RS232. Additional boards can provide single or dual 16-bit, isolated analog outputs, and dual or quad relays for alarm or control. Look for other features that you may need, such as a red or green LED display, and large digit heights. These timers offer digits up to 8" high for a viewing distance up to 300 feet, for example across a factory floor.