Coil Coating Problems: Sensor Accuracy

Coil coating line managers report that they experience three basic problems in solvent vapor monitoring, last week we looked at maintenance issues, this week the focus is on accuracy: 

Sensor accuracy is a problem. Because most analyzers have a wide solvent response factor, they must be checked and adjusted whenever there is a change in the solvents or coatings being run. 

Coil Coating Problems: Maintenance is burdensome

Coil coating line managers report that they experience three basic problems in solvent vapor monitoring, this week let’s address the first one: 

  1. Maintenance is burdensome. Sample lines clog, pumps break down, and analyzer elements become fouled - all resulting in excessive labor and costly downtime. 

Coil coating ovens typically operate at high temperatures, with some zones at over 800°F. This temperature range is needed to cure organic polymer coatings to their substrate materials.

Top 3 Problems in Coil Coating Atmospheres

Coil coating line managers report that they experience three basic problems in solvent vapor monitoring: 

Back to the Basics: Reliability

The Flame Temperature Analyzer has some important reliability features not found in other types:

Back to the Basics: Duct Mounting and Sample Probes

The direct mounting of the analyzer to a process duct has two main benefits: 

  1. eliminates the time delay associated with a long sample line 
  2. makes it easier to keep the sample heated sufficiently to prevent condensation 

Even a very short section of relatively cold sample line can have a very serious effect on the analyzer accuracy and reliability.

Back to the Basics: Response Factors

The most notable feature of the Flame Temperature analyzer is the uniformity of response factors for a wide variety of combustible gases.

Response factors show how a sensor that is calibrated for one particular gas, usually a "reference" gas, will read when exposed to other gases. If two gases both have the same response factor, they respond equally, unless the sensor is non-linear (infrared), in which case linearization of the signal can introduce more error, or less, depending on the individual characteristics of the sensor for each gas.

Back to the Basics: Safety Audits

Due to the special requirements of analyzer systems, a yearly audit should be performed of the following analyzer records:

  1. Installation 
  2. Operation
  3. Maintenance

This should be performed by a person who is an expert in the particular requirements of the analyzer and process, and who may be able to detect potential problems that otherwise might go undetected.

Back to the Basics: Frequency of Calibration

The most reliable method to test the sensor system is to inject a known concentration of test gas, as during calibration, and observe the reading and alarms.

In all analyzer systems, there is a possibility of undetected faults which might disable the analyzer's safety function. Therefore the greater the frequency of calibration and test, the lower the probability of an undetected analyzer fault. 

Automated test and calibration features in computer-based analyzer systems economically allow increased frequency of calibration and test, increasing reliability. 

Back to the Basics: Fault Detection

Analyzers designed to industry standards incorporate malfunction indicators and relay outputs for most potential detectable faults, such as: 

  • low sample flow 
  • downscale reading
  • electrical fault in sensor wire 

It is essential to connect these to the control system so that the operator is notified and the process reverts to a safe condition during an analyzer malfunction. 

 

 

Back to the Basics: Hard-Wired Relays for Danger and Malfunction

While programmable controls and computers provide a great degree of convenience, unless these controls can be shown to conform to strict standards for the use of programmable devices in safety systems, it is preferable to use hard-wired connections for the critical alarm and analyzer malfunction signals. 

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