Manual

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:
R
c =
2200
A + 100
At 20% cutoff:
R
c = 2200 x 0.2 + 100
The value of A which would produce this cutoff is:
A
= 0.04
(since 0.04 = 0.2)
and the input signal would be:
I
= 16mA x 0.04 + 4mA
Operation 19
= 540 kg/min
= 4.64mA