The speed and accuracy of the analyzer depend equally upon the sampling system and the detector. The final development of the worst accidents occurs in seconds. It is part of the last line of defense against fire and explosion. There’s precious little time between the rise in concentration and the explosion. That’s a very good reason to pay close attention to the analyzer’s response time.
10 FACTS ABOUT PREVEX ANALYZERS
the PrevEx is our flammability analyzer for lower flammable limit monitoring (LFL/LEL)
The flame temperature detector measures the heat given off by a flame as it burns combustible gas that diffuses into the flame from the sample.
The small, well-regulated flame heats the tip of a temperature sensor suspended directly above it. The signal produced by the sensor when no flammable vapors are present drives the LFL indicator up to 0% LFL. This failsafe technique is known as a "live" zero because a weakening or loss of flame caused by lack of fuel will generate a downscale malfunction alarm.
Flame ionization is a well-established measurement technique.
The catalytic detector consists of two small electrically heated beads having a finely divided platinum or palladium coating on the surface. A reference bead ONLY responds to changes in:
There are four main detector types used for combustible gas analyzers:
The control of variable ventilation rates can undergo an additional improvement that can result in the detection of certain system faults with a greater margin of safety than the previously discussed methods.
Recipe controls use modeling or prototyping or historical records of process variables to determine limits for detection of unacceptable deviations in the LFL control system.
Variable ventilation controls allow the maximum reduction in ventilation, and thus maximum economy. It also allows some extra corrective action but also one important safety concern: Variable ventilation is based upon the measurement of the L.F.L. concentration and adjustment to ventilation rates through damper or blower controls.
There are two main types:
Once the minimum ventilation requirement is known, dampers must be secured so that ventilation is never reduced below the minimum. The best method is to cut away the damper so that it is not possible under any condition to reduce the ventilation rate to an unsafe level. Manually adjusted stops, and sometimes even welded stops, have been found to be insufficient to prevent accidental loss of ventilation due to incorrect damper settings.
There are several fundamental safety precautions which should be applied to all dryer designs.
