Tachometers for safe and hazardous areas

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The measurement and display of rotational speed is a common engineering requirement in process plants. To satisfy this requirement the new range of BEKA field and panel mounting Tachometers produce a speed display in engineering units from most types of pulse output rotation sensor. For maintenance purposes they can also display how long the monitored machinery has been operating.

BEKA field and panel tachometersFig 1 BEKA field and panel tachometers

Although any rotation sensing technology may be used within process measurement applications, inductive, capacitive and optical proximity detectors are common. These are rugged, easy to mount, 2-wire devices with an internationally accepted NAMUR current output. Widely available from multiple manufacturers they greatly simplify sensing.

General purpose tachometer systems are simple to design and install. It is only necessary to configure the tachometer to operate with the selected sensor and to calibrate the tachometer to display rotational speed in the required engineering units. The same requirements exist for installations in flammable gas and combustible dust atmospheres, but the tachometer and sensor require certification to ensure safe operatioin in the explosive environment.

Intrinsically safe BA317E-SS mounted in an Ex e enclosureFig 2 Intrinsically safe BA317E-SS mounted in an Ex e enclosure.

Whilst various explosion protection techniques may be used, protection by intrinsic safety Ex i offers significant advantages, including safe adjustment and maintenance while the tachometer and sensor are powered.

The new BEKA tachometers include internationally certified intrinsically safe models for use in gas and dust environments in addition to the general purpose instruments.

The range also includes a rugged panel mounting intrinsically safe tachometer in a stainless steel housing which has certified front of panel protection. This novel instrument may be safely mounted in an Ex e or Ex p panel enclosure without invalidating the certification of the enclosure as shown in Fig 2. The tachometer requires powering via a Zener barrier or galvanic isolator which may be located in the safe area or in a local Zone 2 enclosure.

For applications in lower risk Zone 2 environments, the Ex nA certified BA317NE tachometer, which does not require a Zener barrier or galvanic isolator, can also be mounted in an Ex e or Ex p panel enclosure without invalidating the certification of the panel enclosure.

For more information please see our tachometers webpage.