Control Example
While monitoring for machinery protection is the primary application for the HPL110A,
it is also suitable for simple two-point control regulation applications by using the
Hysteresis function included in the unit.
A possible control example might be where the HPL110A is monitoring the power
consumed to mix a slurry and the relay output is used to add liquid if the slurry becomes
too viscous.
This is shown graphically in Figure 2.2. Power surges when the motor is switched
on and the Ts function inhibits monitoring until the motor settles at time 2.5.
Once Ts is completed, the high power alarm becomes active and a hysteresis band
(programmable) is shown under this alarm level. At time 5, the mixing power rises
above the L1 Max. Limit and, after the Tr1 trip delay times out, the alarm is activated
and the relay switches.
In this example, the relay controls the addition of liquid to the slurry and the power
gradually drops as liquid is added until at time 7, it has fallen below the hysteresis
band for the L1 Max. Limit. At this point, the alarm relay is automatically reset and
the addition of liquid is stopped.
Typical applications include the continuous control of mixing, crushing and grinding
processes. Hysteresis is also available on the L2 Min. limit in the same manner
(not shown).
Max. Limit
L1
100%
P (%)
Ts
t
Tr1
Power On
Relay On
0 1 2 3 4 5 6 7
P = f (t)
5%
6
F i g u re 2 . 2
