As mentioned earlier, relay timers are simulated in firmware, operating as a background process called by a timer interrupt. ProXR controllers use an external system clock to maintain a 3% timing accuracy, not to be confused with a real time clock (RTC). Since relay timers are derived from the system clock, it would stand to reason that relay timers maintain a 3% accuracy as well. However, the CPU that powers ProXR controllers handles many interrupts on a priority basis, which can further deviate the accuracy to the timers. ProXR relay timers are best suited for applications that do not require precise timing. For instance, activating a porch light for 30 minutes, or closing a gate after 2 minutes, or ringing a school bell for 20 seconds. These applications don’t really care if the timing is off by a few seconds.
Perhaps one of the most useful features of Relay Timers include the timer calibration function. Timer calibration can be used to define the length of a second, as seen by the timer. By lowering the timer calibration value, the timer can be accelerated. Similarly, increasing the timer calibration value can greatly increase the length of a single second. This feature is particularly useful if you need to control timing operations at a higher resolution. Some customers have lowered these values to increase timing precision with great success.
Users may experiment with timer calibration in the “Timer Calibration” control panel. This control panel allows you to experiment with activating 1, 8, or 16 timers simultaneously, testing short and long durations so you can see the actual effects of your settings over longer time periods. Please note, since computers are interrupt driven, timing accuracy of the software is limited.
Be sure to write down your favorite calibration setting, as it will be necessary to use the “Device Configuration” control panel to store your timer values.