APC AXFA11G Function or, Determining rate limit value and dead time, Example 1 Step input

[J20: Flow Direction] Setting of the flow direction Upon shipment from the manufacturing plant, the system is setup such that flow in the same direction, as shown by the direction of the arrow mark on the flowtube, will be measured as forward flow; however, this parameter can be used to set “Reverse” so that flow in the opposite direction to the arrow mark will be treated as forward.

Note: This function does not apply to measurement in both the forward and reverse directions, al- though this can be setup using by selecting “Fwd/Rev Ranges” from either F10: SO1

Function or		.
Setting		Function
Forward	Forward direction corresponds with arrow mark
Reverse	Forward direction is opposite to arrow mark

T0638.EPS

[J21: Rate Limit] Setting of the rate limit value

￿This parameter is used in situations where sudden noise cannot be eliminated by increasing the damping time constant.

￿In situations where step signals or sudden noise signals caused by slurries or the like are entered, this parameter is used to set the standard for determining whether an input corresponds to a flow measurement or noise. Specifically, this determination is made using upper and lower rate limits and using the dead time.

￿Rate limit values are set using a percentage of the smallest range. The range of deviation per one calculation cycle should be input.

[J22: Dead Time] Setting of dead time

This parameter sets the time for application of the rate limit, and if a value of 0 is set, the rate limit function will be terminated.

NOTE

Determining rate limit value and dead time

Rate limit value:		Dead time (T0):
Determines the level for output		This is to be determined using the
fluctuation cutoff. For example,		output fluctuation width. If noise
if this is set to 2%, noise above		exceeds the dead time as shown in
2% will be eliminated as shown		the diagram below, the dead time
in the diagram.		should be made longer.
				T0
	2%
	2%
			T0
					F0616.EPS

6.PARAMETER DESCRIPTION

￿Signal processing method:

A fixed upper and lower limit value is setup with respect to the primary delay response value for the flow rate value obtained during the previous sam- pling, and if the currently sampled flow rate is outside these limits, then the corresponding limit is adopted as the current flow rate value. In addition, if signals which breach the limits in the same direction occur over multiple samples (i.e., within the dead time), it is concluded that the corresponding signal is a flow rate signal.

Example 1: Step input
				Input: 0 to 10%
				Damping time constant: 3 s
				Dead time: 3 s
Step signal				Rate limit value: 1%
10%
	Flow rate value			63.2%
	after rate limit
	processing
(a)	(b)	(c)		(d)Flow rate value after
1%				damping
	100		225	Number of signal samples
	Dead time: 3 s			F0617.EPS

(1)In comparison with the previous value at (a), it is determined that the signal is in excess of the rate limit value and the response becomes 1%. How- ever, the actual output applies damping, and therefore the output turns out to be as indicated by the solid line.

(2)Subsequent flow values within the dead time zone correspond to signals of post-damping flow value + rate limit value (1%).

(3)Since input signals do not return to within the rate limit value during the dead time, it is determined at

(c) that this signal is a flow rate signal.

(4)The output signal becomes a damped curve and compliance with the step signal begins.

Three seconds after determination of a flow rate signal in the above figure, a level of 63.2% is reached.

Example 2: Slurry noise
		Input: 0 to 10%
	Slurry noise	Damping time constant: 1 s
	Flow rate value	Dead time: 1 s
		Rate limit value: 1%
	after rate limit
+1%	processing
-1%		In the figure on the left, it is
		determined that the slurries
	Flow rate value after damping	noise signal is not a flow rate
		signal.
	Dead time: 1 s	Time
		F0618.EPS

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