Emerson Process Management 8732 manual How Does It Really Work?, Flow Rate, Time

Reference Manual

00809-0100-4663, Rev BA January 2010

Rosemount 8732

This software technique, known as signal processing, “qualifies” individual flow signals based on historic flow information and three user-definable parameters, plus an on/off control. These parameters are:

1.Number of samples: The number of samples function sets the amount of time that inputs are collected and used to calculate the average value. Each second is divided into tenths (1/10 ) with the number of samples equaling the number of 1/10 second increments used to calculate the average. Factory Preset Value = 90 samples.

For example, a value of:

1 averages the inputs over the past 1/10 second 10 averages the inputs over the past 1 second

100 averages the inputs over the past 10 seconds

125 averages the inputs over the past 12.5 seconds

2.Maximum Percent Limit: The tolerance band set up on either side of the running average, referring to percent deviation from the average. Values within the limit are accepted while value outside the limit are scrutinized to determine if they are a noise spike or an actual flow change. Factory Preset Value = 2 percent.

3.Time Limit: Forces the output and running average values to the new value of an actual flow rate change that is outside the percent limit boundaries, thereby limiting response time to real flow changes to the time limit value rather than the length of the running average. Factory Preset Value = 2 seconds.

How Does It Really Work?

The best way to explain this is with the help of an example, plotting flow rate versus time

Figure D-1. Signal Processing .

Flow
Rate
	Max
	%
	Limit
Time Limit
12 Samples = 1
Second	Time

D-3