Relay Actuation In Proportional Control; Cycle Time - Hach LANGE si629 P Bedienungsanleitung

4. Operation

Relay actuation in proportional control

pH 4
A L A R M
100%
50%
0%
With proportional control there are 3 zones:
Tolerance zone
This zone corresponds to values considered as
correct, hence tha relays are not activated.
Proportionl Band
This is the zone where the control is carried out.
In this band the relay is activated during a time
(tON) proportional to the distance between the
reading and the tolerance band. The rest of time,
inside the relay cycle, the relay is desactivated
(tOFF). Hence the cycle time = tON + tOFF.
Alarm zone
The relay is activated permanently and the alarm
will be activated when surpassing the time pro-
grammed in Programming Alarm (see page 17).
The current output will be fixed at 22 mA.
IMPORTANT:
• The minimum efective time of relay activation is 20% of the cycle time. It means that for a cycle time
of 10 sec. despite that the activation time (tON) is 0.5 sec., the relay will be activated during 2 sec.
• If too short cycle time is programmed, the pumps with induction motor can give problems with the
proportional control of the si629 P. The time of relay activation can be insufficient to ensure a stable
motor regime. If so, the generated current pick after being repeated several times may burn the en-
gine or its control relay.
The electrovalves and the membrane pumps do not present this problem.
si629 P_HACH_LANGE_Ed.0510.indd ANG:25 si629 P_HACH_LANGE_Ed.0510.indd ANG:25
5 6 7
PROPORTIONAL
T O L E R A N C E
BAND
p H V A L U E
T E N D E N C Y
RELAY 1
8 9
PROPORTIONAL
A L A R M
BAND
RELAY 2
Relay

Cycle time

For example:
Optimum value: 7
Tolerance zone: ± 1pH
Proportional band: 1 pH
Cycle time: 10 sec.
pH 7 ±1, zone without any control
pH 8, start of the control
pH 8,5, tON = 50% of cycle time, in this case 5 sec.
pH 9, start of alarm zone, relay is activated perma-
nentemently.
10
Time (sec)
25
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