How do I measure flow within an environment with an explosive atmosphere

In this article we bring you some of the more interesting and topical application challenges posed to Titan Enterprises and the solution we provided. Don’t hesitate to send your flow metering application requirements to us here, to see how we can help you.

Q: How do I measure flow in an area with an explosive atmosphere ?

A: In an area where an explosive mixture of vapour or powder can be present either continuously or intermittently, steps must be taken to minimise the risk of an ignition source within this space. There can be no high temperatures, voltages or the capability of generating a static or frictional spark. Workers within the area must also comply by wearing suitable clothing and carrying only ATEX approved electrical devices.

Because of the wide variety of scenarios that may produce an environment with an explosive atmosphere there is no one method of installing a flow meter in such an area. Here though are some flow metering options to consider.

1. Use a totally mechanical flowmeter: This removes the requirement for any electrical input into the device although there may still be temperature considerations. Meters in this category include variable area flow meters or gear flow meters with mechanical totalisers.

2. Use a passive device: Simple passive devices such as switches cannot in themselves induce or generate a spark. Obviously any instrumentation connected to these components must be intrinsically safe also. Passive switch devices have carefully designed circuits to ensure that there is insufficient energy to discharge a spark or that any component failure would not cause another component to overheat.

3. Use a device with remote electronics installed in a “safe” area: such devices have the power transmitted through them limited by a barrier at the safe/hazardous environment interface. This limits the amount of energy that can be transferred into the hazardous area. The benefit of this approach is that you can use standard instrumentation as it can be installed in the safe area.

4. Use a flow meter fitted with an approved active sensor: An active sensor is a detection device that requires input energy from a source other than that which is being sensed. Examples of active sensors include Namur, Hall Effect and Coil devices. In this instance the sensor itself is approved for use in the hazardous area but the power to it must be controlled.

5. Install your flowmeter in an explosion proof box: In this option the flow meter is placed in a controlled environment container. This ruggedized box is able to contain any explosive event spreading to the “outside” world. This is far from ideal and a relatively expensive method but on occasions where no other flow measurement solution is possible, it may be the only answer.

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