Yokogawa 414 Batch Controller Bedienungsanleitung PDF herunterladen (Seite 21)

3.3.2 The Cutoff Point

Because many transducers do not always exactly transmit 4mA (0mA, 1V or 0V)

when they are at zero rate, it is often necessary to define a rate below which no

integration takes place. This is termed the cutoff point and is programmed as a

percentage of the Span, S.

For example, if S = 2200 kg/min with an offset of 100 kg/min in a square law

system, and the cutoff point is set at 20.0%, the actual cutoff rate Rc can be

determined as follows:

The cutoff rate is defined as:

c =

2200

A + 100

At 20% cutoff:

c = 2200 x 0.2 + 100

The value of A which would produce this cutoff is:

= 0.04

(since 0.04 = 0.2)

and the input signal would be:

= 16mA x 0.04 + 4mA

Operation 19

= 540 kg/min

= 4.64mA

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Yokogawa 414 Batch Controller Bedienungsanleitung Seite 21