Voltage measuring range
Voltage measurement range supported by the device.
Many modern control relays are equipped with digital displays, which can display, including current voltage; this parameter specifies the operating range of the built-in voltmeter. In this case, the voltage measurement range can be noticeably wider than the difference between the smallest minimum and the largest maximum shutdown threshold (see below). This allows you to use the relay also for online diagnostics of the network status.
For a current relay (see "Device") in this case, the range of operating voltages can be given directly — the voltage at which the device can normally perform its functions.
Measurement accuracy (±)
Measurement accuracy provided by the device. In this case, different types of measurements may be implied, depending on the purpose of the relay (see "Device"). Note that in
power relays and multifunctional devices, the measurement accuracy for voltage and current is usually the same, and a common parameter is given in the characteristics for them.
Accuracy is indicated by the maximum measurement error provided by the device. First of all, the operation accuracy depends on this parameter: the lower the error, the smaller the actual deviations from the specified operation parameters. For modern control relays, an indicator of 3 – 5% is considered acceptable, 1.5 – 3% is not bad, 1 – 1.5% is good, less than 1% is excellent. However, in fact, it is also worth choosing according to this parameter, taking into account how sensitive the connected load is to the accuracy of the specified operation parameters.
Also note that many modern relays are equipped with digital displays that can display various parameters. In such models, the measurement accuracy also determines the accuracy of the readings of such a built-in "tester".
Off time (upper limit)
The device shutdown time on the upper limit of voltage or current. This is a kind of "reaction time" of the relay: the period of time between reaching the upper limit and turning off the protected network segment.
The lower this value, the more advanced the protection will be, the lower the probability of failure of sensitive devices due to untimely operation of the relay. Note that a short reaction time in this case is especially important, because too high a voltage or current is a serious danger to any device.
Lower cut-off limit
The lower voltage shutdown limit provided in the relay; when the voltage drops below this value, the device turns off the power to the protected network segment. Usually, this limit can be adjusted, and the specifications indicate the range of such adjustment.
Although the main danger for various electrical appliances is increased voltage, many devices do not tolerate too low voltage. Therefore, modern voltage relays provide shutdown not only on the upper, but also on the lower threshold.
Upper cut-off limit
The upper voltage shutdown limit provided in the relay is the voltage, when exceeded, the device turns off the power to the protected network segment. Usually, this limit can be adjusted, and the specifications indicate the range of such adjustment.
