Electronic monitoring relays from Pilz

A new feature on the PMDsigma units is the ability to set values very simply and then save them on a chip card. Settings can therefore be copied to other units, which is especially useful for manufacturers of series machines or when replacing units in the field (on site). Menu-driven parameter setting is easy, quick and error-proof thanks to the plain text display and a turn-and-click encoder. Once set, the unit's cover can be locked closed to discourage unauthorised tampering. The LCD display, together with six front-panel LEDs, provides user-friendly diagnostic information.

The first unit in the new generation of PMDsigma relays monitors true power and is approved for applications worldwide. This PMD s10 unit will typically be used to provide an early warning of hazardous plant conditions, with no requirement for additional sensors. This compact (45mm wide) unit measures true power to give an indication of the motor load, which can be used to derive values for fill level, air pressure, hydraulic pressure, torque or fluid viscosity, for example. In addition to providing an analogue (0 or 4-20mA) output that is proportional to the true power, the PMD s10 also monitors overload and underload thresholds, with an output signal sent to a PLC or via the integral relay.

Various types of load up to 11kW can be monitored directly, or larger loads can be monitored using current transformers. The PMD s10 processes frequencies from 0-1000Hz, so it is very versatile and suitable for both DC and AC motors, including frequency-controlled motors. Motor start-up and transient power fluctuations can be suppressed in order that high inrush currents do not affect the unit. To make configuring the unit even easier, the measuring range is set automatically.

During operation, the display can show values such as current and power consumption. An integrated counter can record the operating hours and number of cycles; this data can be used as part of a preventive maintenance regime to minimise unplanned downtime and unscheduled repairs. Another useful feature is that peak values can be stored and called up via the display. Intelligence built into the electronics ensures that the monitoring relay is fail-safe.

One of the key applications for the PMD s10 is in early warning systems to detect the onset of potentially hazardous plant conditions - without the need for additional sensors. For example, blocked filters or worn bearings can be identified before they lead to failure. This helps to avoid expensive mechanical damage, downtime and hazards to personnel.