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IP258
24
7.0 PROGRAMMING THE MSM400 FUNCTIONS
DUTY (MODE)
DESLUDGE MODE.
There are several methods of starting, stopping, overriding and stopping early a de-sludge operation. The desired
options can be selected in the SETUP – DUTY (Mode) – DESLUDGE menu. The following table explains the various
options.
(PV = process value i.e. % suspended solids)
Start on Stop on Stop if Do not start if
PV above level* PV below level** PV below level** Digital i/p 2 low****
Digital i/p 1 low *** Digital i/p 1 low *** Digital i/p 1 low ***
Time Max Time
Normally relay 1 is used for control purposes. Relay two is normally the alarm relay.
If selected, the desludge operation defaults to “Start on”– Time, “Stop on”– PV below a level.
“Do not start if” and “Stop if” are set to “none” (i.e. in default conditions these do not affect the desludge
operation).
* Above level is above Relay 1 or 2 On Point
** Below level is below Relay 1 or 2 Off Point
*** Digital input 1 low for 1 sec, 2 sec, 5 sec, 10 sec, 15 sec, 20 sec, 30 sec, 40 sec, 50 sec, 60 sec, 90
sec, 120 sec, 180 sec, 240 sec & none
**** Digital input 2 low for 1 sec, 2 sec, 5 sec, 10 sec, 15 sec, 20 sec, 30 sec, 40 sec, 50 sec, 60 sec, 90
sec, 120 sec, 180 sec, 240 sec & none
The min and max times described in Set point operation also apply in de-sludge mode.
If it is required to set the control unit up to Start on Time then 4 parameters can be set up:-
1. Start time 1
2. Time interval 1
3. Start time 2
4. Time interval 2.
(Start time 2 and interval 2 default to not used.)
The time interval indicates the interval between de-sludges.
Start time 1 indicates the time of the first de-sludge operation. A de-sludge will always happen at this time each day
independent of the time interval.
Start time 2 indicates the time of another fixed de-sludge time.
If either of the start times are set to 0:00 then the interval associated with that start time is not used.
If both of the time intervals are set to 0:00 then de-sludge only occurs at the start times.
The following table shows the default and limits of the time desludge operations.
No. of operation. Set in Default value Max value
(hrs & mins.) (hrs & mins) (hrs & mins)
Start time 1 hh:mm 8:00 23:59
Time interval 1 hh:mm 1:00 24:00
Start time 2 hh:mm 0:00 23:59
Time interval 2 hh:mm 0:00 24:00
Example:
In this example it is required to control the desludge operation as follows: Relay 1 will be used to open a discharge
valve. Desludge cycles should start at fixed intervals. Each desludge cycle should stop on detection of thin sludge,
thus preventing unwanted transfer of clear liquor. The “Stop if” function will also be used to stop the desludge using
a digital input (i.e. an external trigger.). from a pump protection switch if the pump should fail. Typically in this
example the sensor is mounted close to the bottom of a primary tank or in the discharge line.