Article Archive
Eliminating Sensor Drift
Crowcon Introduces Automatic Gas Calibration
Vol. 21 No. 1

Gas detection instruments are used to detect the presence of toxic and combustible gases, as well as oxygen deficiency or oxygen enrich-ment, to detect the explosive hazard before a fire occurs. Unfortunately, detectors are sometimes subject to "drift," a gradual degradation of the sensors that can make readings unreliable.

One method for verifying instrument accuracy is a "bump" test which verifies calibration by exposing the instrument to a known concentration of test gas. The instrument reading is compared to the actual quantity of gas present (as indicated on the cylinder). If the instrument's response is within an acceptable tolerance range of the actual concentration, then its calibration is verified.

The International Safety Equipment Association (ISEA) recommends that a bump test or full calibration of direct-reading portable gas monitors should be made before each day's use in accordance with manufacturer's instructions, using an appropriate test gas. ISEA recommends more frequent testing if environmental conditions that could affect instrument performance are suspected, such as sensor poisons.

Crowcon Detection Instruments has introduced an automatic calibration device for use with its Tetra, Triple Plus Plus and Gasman personal gas detector products. CheckBox IMH (Instrument Management Hub) automates the calibration and bump testing of portable gas detectors, reducing operation time and cost. The station can test up to 10 Crowcon detectors at once, calibrating and bump testing then uploading data files as required.

Alan Skinner, business development manager for Crowcon's fixed gas detection systems, was on hand with the new device at the 2005 National Fire Protection Association Conference & Exposition held last June in Las Vegas.

"Before Crowcon, each of these portables would have to be manually calibrated one at a time," Skinner said. "Since it was done manually, there was a high labor cost involved. Now the employee can just set the instrument in the CheckBox device and switch it on. Then you walk away while it calibrates each of the 10 portables in the device, making all the adjustments automatically without being touched."

CheckBox also eliminates the human error factor, Skinner said.

"We try to make calibration and bump testing as simple as possible when using the Crowcon Portable devices," Skinner said. "Crowcon makes it very simple for the operator with a one-button operation,. That meant man-hours of training and, of course, downtime for the instrument."

By allowing both pumped and non-pumped detectors to be calibrated and tested using the same procedure, the CheckBox greatly simplifies the whole instrument management process, Skinner said. CheckBox is linked to a PC so all data is permanently recorded ensuring traceable records and can be downloaded and saved for future access. Gas lot or batch numbers and expiration dates can also be entered into the CheckBox records and printed on certificates.

The station supports up to eight gas inlets. One inlet provides air for zeroing, with the remaining inlets allowing up to seven different calibration gases (or a combination of gas mixes) to be tested. When testing standard four-gas monitors using flammable oxygen, hydrogen sulfide and carbon monoxide the device supports the use of quad-mixed calibration gas, minimizing calibration time and gas usage.

CheckBox optimizes gas bottle usage between single and mixed gases by automatically determining the best gas bottle or combination of bottles to calibrate each detector. It does this by comparing the sensor combination to the gas bottles attached to the system.

CheckBox calibrates personal detectors such as "Gasman," small enough to fit in the palm of your hand. Another new gas monitor product from Crowcon is designed to be exactly the opposite. The Detective is intended for temporary gas monitoring installation, designed specifically for turnarounds or other short-term operations. The device will monitor for up to four different gases simultaneously.

"Plant Turnaround can be dangerous," Skinner said. "You've got employees working in areas where the fixed gas detection system may be switched off. The Detective is a transportable device with a 24-hour battery that serves as a standby system."

Although portable, the Detective is too big to be easily disregarded. An employee might set his personal detector down and forgetfully walk away, Skinner said. The sound of heavy equipment in operation can easily cover the sound of an alarm from a small device placed far away. The Detective comes with a flashing cluster of lights and a 101 decibel audible alarm that can not be ignored even in a noisy plant setting.
Detective units can be linked together using RS232 cable to protect a wider area. Those units will also connect to a wireless system that transmits data back to a central control room.

Next to be announced from the Crowcon product pipeline is a fixed system hydrogen sulfide detector designed for offshore drilling platforms that comes with a two-line transmitter. Skinner said the new product would be officially announced by Crowcon soon.

 
 

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