Frequently Asked Questions


Is it appropriate & safe to use current sensing to prove fan performance?

Whilst Caledonian advocates the use of true volumetric air proving when at all possible utilising differential pressure sensors or anemometer technology, we have conducted a series of experiments to determine whether an indirect method, and more specifically using current sensing, can be safely employed.

The following three basic aspects have to be considered if an indirect method is to be deemed safe:

  • Can a safe start test be made?  i.e. is the sensor working
  • Can a rising set point be set?
  • Can a falling set point be set?

We found in our tests that all of these criteria could be met and that an indirect current sensing methodology could be used safely in situations where direct methods are inappropriate or even impossible.

The chart to the right, which plots Air Flow against Motor Current drawn in Amps, clearly shows that there was, for our test ventilation system, a specific range of current drawn when the system was working correctly.

We named this the ‘Effective Range’

When employing this test in the ‘real world’ the effective range has to be determined for each installation so that the controller and sensor can be calibrated.

Having done this correctly, we found that using the indirect current sensing method is as reliable and safe as the more traditional direct methods.


Please call us to get your copy of our application notes.


I can't afford to close the kitchen, can the system be overridden?

Firstly. it has to be said that the HSE, Advantica, CORGI and the rest are completely against the bypass of any safety device. A ventilation-gas interlock is no different, wherever it is used or whatever the commercial considerations. We believe that there is a good argument to say that bypassing any safety interlock could possibly be a criminal act.

Owners think that kitchen interlocks should be a special case – just because the restaurant would lose money if it had to close! Often they don’t think that the ventilation system is really going to cause a hazard.

What happens should the ventilation system be defective? 

Firstly, it would become uncomfortable for the staff, although this might not actually be noticed by them acting on the principle that 'if you can't stand the heat, get out of the kitchen'.

At the same time as the gas appliances consume the oxygen (O2) in the air they produce a proportional amount of Carbon Dioxide (CO2) This increases the effect of low O2 by adding the suffocating factor of CO2. When the O2 has fallen by only a small amount the gas  burners will initially increase their CO2 emission (called the excess air depletion stage) then after a short period Carbon Monoxide (CO) will be produced. Due to the human body's rapid absorption of CO it is one of the deadliest of gases.  It is a complete fallacy to think that humans can smell that something is wrong, O2, CO2 and CO have no smell. Often other contaminant gases associated with a lack of oxygen can be detected by the human nose but usually this is too late. Many kitchen workers suffer from mild oxygen starvation and CO & CO2 ingestion. The symptoms of headaches and nausea are often ignored.

The EMX50 Fan Safeguard Control is NOT fitted with any kind of override. Instead, the control has a long MTBF. In the unlikely event that it should fail, it can be replaced in seconds due to its modular design.


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