Is your Plant as tight as you think? Leak Detector for extremely toxic Gases: Product Family completed by a high Range Version

The problem was how to locate small leaks in chemical plants where a combination of different substances is present in the background. For this application a gas detector was requested which could detect the target gas at ultra low levels, without responding to other gases.

The idea was to use an electrochemical cell as sensor. This sensor technology will only respond to substances producing a non-soluble salt with the working electrode material. It will not be affected by humidity, hydrogen, or hydrocarbons. To keep the sensor electrically neutral and to stimulate the electron flow, the counter electrode is kept busy producing water.

A disadvantage of this method in the past has been high response time, when being compared to physical methods of detection. With diffusion, the transformation of material on the working electrode just takes a while.

Intensive research has proven that the process of material transformation at the working electrode can be accelerated by forcing the gas to access the sensor, instead of entering by diffusion. It seems that the process of approaching the active area at the working electrode is the most time consuming step.

Compur Monitors has developed an instrument with an integrated pump and a flow chamber optimized for leak detection.

The result is a leak detector that would respond to gas almost as fast as a detector using a physical method of detection.

Leak locating strategy Move the intake of the sampling probe slowly along the surface being inspected. An increasing measured value indicates you are approaching a leak. The measured value is indicated as a digital figure or a bar graph. The control tone and LED will increase their alarm frequency in ratio to the measured value, similar to a Geiger counter.

The Tracer protects itself from being poisoned. If the measured value goes out of range the pump will turn off and will not start again until the concentration falls below 95% of the range.

As the leak detector will eventually be exposed to very high concentrations, it must not be used as a personal monitor. To prevent the Tracer from being used as such it does not display an actual concentration. The display shows only a numerical value or bar graph proportional to the amount of gas detected.

For use in dark areas the display features a backlight.













The Tracer is available for the following gases: Cl2, ClO2, COCl2, HCl, HCN, H2S and NO2.

Field test results The first tests in plants have proven that an ultra-low measuring range is not always required. In analyser cabinets for instance we found concentrations above the measuring range causing the Tracer to shut off to protect its sensor. So we could detect the leakage but not locate it.

Now we had to square the cycle: We did not want to renounce the sensitivity of the Tracer. However we had to increase the measuring range drastically to locate leaks where the background concentration had accumulated. We rejected to just change the amplifier adjustment to prevent the sensor from poisoning.

We chose another approach: Since the electrochemical sensor operates like a gas - operated battery, every molecule hitting the working electrode delivers or consumes one or more electrons. If we could restrict the number of gas molecules accessing this electrode being a "molecule counter", we would be able to decrease the signal generated. We decided to use orifices restricting gas diffusion to the electrode.

We needed to design the orifice in such a way that the user would be able to increase the measuring range by a factor of 20 without changing the amplifier adjustment. This was achieved through extensive testing. Now the user can in an instant replace the LOW range sensor by a HIGH range sensor and so cover a measuring range from the low ppb range up to the two digit ppm level without doing any adjustment!

We returned to the plant with our new model, the HIGH range Tracer, it showed we had chosen the right measuring range. When we approached a leakage, the display would go up to the mid of the range. Moving the Tracer sample probe along tubes and fittings it was now easy to locate leaks. Weak points in many installations were taps, fittings and compression glands of valves. Even Teflon or PTFE sealing washers seem to be subject to corrosion after long term exposure to halogens.

Another task was to check the bursting disc manometers. For this application the LOW range Tracer was the better choice. The smallest leaks in a fitting or tube connecting a control manometer can lead to a malfunction of the burst disc.

Since the initial field tests, the dual range Tracer has become a well - received tool for leak detection. The Tracer is ultra sensitive where it needs to be and robust when detecting leaks in cabinets and containments.