Why Measuring Flow is a Difficult Task: Damping the Signal (Part 1 of 2)

E-Zine May 2014

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In either case, various techniques can be used to reduce the noise component of the signal. One method is to dampen the signal. This method will usually work in most applications, because the noise will be reduced as the damping is increased. Also reduced is the ability of the instrument to measure the process in a timely manner because the response time of the damped instrument will increase. Typically, when more than a small amount of damping is necessary to reduce noise, there is another problem. In these applications, increasing damping can mask the real problem and could adversely affect the process.

In flow measurement, damping is usually required to achieve a usable signal for a controller. The user must then decide where the damping will be installed -- in the control system, in the flowmeter or both. Damping performed in the control system is usually readily accessible, and its values can be documented as part of the control system documentation. However, the damping algorithms in the flowmeter are likely to be superior to the generic algorithm(s) found in the control system.

When damping is installed in the flowmeter, the damping value is typically not readily accessible. The damping value(s) should be appropriately documented so that the information is available when the flowmeter is repaired or replaced. Further, when large amounts of damping are added in the flowmeter, changes to the flowmeter and/or process that cause the flowmeter itself to become unresponsive may be masked. Thus, there appears to be no one best location to implement damping.

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From Flow Control (August 2002)

ISSN 1538-5280