CONTROL PARAMETERS
CONTROL SCHEMES*
PARAMETER DESCRIPTION RO CL
1) RES CTRL GAIN
2) RES CTRL LIM
3) FIXED LAG TIME
4) VAR LAG TIME
5) FLOW @ VAR LAG
Residual Control Gain establishes how aggressively the controller
responds when making corrections to maintain the residual Set
Point level. The higher the gain is set, the larger and more
frequent the corrective action will be. Too high a setting may lead
to excess “up and down” adjustments to the feed rate, whereas,
too low a setting may cause slow, insufficient adjustments. The
setting is in percentage (0.1 to 100). Factory set at 20%.
Residual Control Limit places a “band” around the waterflow
(primary) signal to prevent the over (or under) feeding of gas due
to a possible drifting, inaccurate, residual (secondary) signal.
e.g. - Using a 50 PPD system. If the water flow units are in
percentage and the present water flow is 40 %, the primary feed
rate would be 20 PPD. Therefore, a 10% residual control LIMIT
will restrict the OVERALL gas feed rate to +/- 10% of the primary
feed rate. Since 10% of the valve’s 50 PPD capacity is 5 PPD, the
output would be limited to a range of 15 to 25 PPD.
NOTE:
The setting range is 0 to 25%. Factory set at 20%.
IMPORTANT:
As explained in Section 2B, the TOTAL system
lag time (T1 + T2 + T3) refers to the time from when the chemical
solution exits the ejector assembly until the time that the
residual water sample reaches the wet cell of the residual
analyzer. Depending on the Control Scheme, the lag time will
be either FIXED or VARIABLE. The final three Control
Parameters listed below are used to provide the necessary
data for the controller to calculate, and compensate for the
lag time prior to making adjustments. NOTE:
An effective and
relatively easy method of setting these parameters is
explained in detail in the next section (SETTING THE LAG
TIME).
The total system lag time becomes FIXED when there is no
variation in the water flow (T2). Therefore, this parameter applies
strictly to Residual Only Control which has a FIXED water flow.
The time setting is in seconds.
Variable Lag Time. The total system lag time is variable only when
the water flow (T2) is variable. Compound Loop Control systems
have variable water flow, therefore,variable lag time. The time
setting is in seconds.
Flow at Variable Lag refers to the rate the water is flowing when
the total lag time is measured. This value sets the necessary
“span” to establish the range of minimum to maximum lag times.
The value MUST be set based on the Flow UNITS and Flow
RANGE selected in the Configuration Mode.
YES
N
O
YES
NO
NO
YES
YES
NO
YES
YES
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