Back to the Basics: Accuracy and Response Time Requirements

Accuracy and response time are closely related. The purpose of the analyzer system is to produce an alarm before the solvent concentration can increase to an unsafe level. This implies that the alarm is given in sufficient time to take effective corrective action. 

There are two cases to be considered: 

  1. the steady-state (time invariant)
  2. the transient (dynamic) 

This week let's look at the steady-state:

Back to the Basics: Time to Alarm

Each drying process has a unique rate of solvent increase in the normal and upset conditions. The potential maximum rate of solvent concentration increase should be estimated, so that the analyzer has time to generate an alarm, and the method of corrective action has time to reduce the solvent concentration, before a flammable or explosive limit is reached in the dryer. 

Some of the factors include: 

Back to the Basics: Total Analyzer System Response Time

The response time of the analyzer system, including all components in the final installation, is so critical that it should be given careful attention. 

One useful method of testing the system time response of the analyzer is to inject test gas directly into the end of the probe inside the process, and to obtain the time that it takes for the alarm to sound. The test gas concentration should be equivalent to at least 10% LFL above the high alarm point.