EMC INDUSTRIAL GROUP LTD Internal Signals
MW93A_IM_ALL_SV6.09f_en 38/59
Limit 2
Q23521 limit 2 source (modbus address of signal) 8360, g7
Q23522 limit 2 mode 8364, g7 low limit = 1
Q23523 limit 2 delay 8362, g7 0.00 s
Q23524 setpoint 2 8332, g7
Q23525 setpoint 2 preact 8366
Limit 3
Q23531 limit 3 source (modbus address of signal) 8340, g7
Q23532 limit 3 mode 8344, g7 fill control = 4
Q23533 limit 3 delay 8342, g7 0.00 s
Q23534 setpoint 3H 8334
Q23535 setpoint 3L 8346
Events/Alarms/Faults
Various events can be triggered by the inputs (eg to capture the weight) or automatically when certain
situations are detected by the transmitter. Each event has an ID and produces a value.
Q2361 event ID 8780, g8
ID of most recent event.
Q2362 event value 8782, g8
Value of most recent event.
Q2363 last alarm event 8784, g8
Value of most recent event.
Q2364 alarm list (press EDIT to view list of all possible alarms) 8920, g8
Scroll through a list of all possible alarms.
Q2365 delay time [0.00 to 300.00] 8458, g8 0.00 s
A timer used by the macros.
Q2366 healthy options 8456, g8 0
Selects which faults control the healthy signal.
Q2367 fault delay 8486, g8 10 s
Delay used for belt speed, low platform weight and error limit faults.
Q2369 fault options 8454
Allows selected faults to not raise an alarm.
Control
The belt speed is controlled to keep the measured flowrate as close as possible to the flowrate set-
point. The technique used to determine the belt speed demand is a combination proportional and inte-
gral control ie. PI control for short. These variables affect the PI control characteristics.
PI settings
Q23711
proportional band (increase if flow control is unstable)
8460 220.0 %
This is the proportional band. Generally, the larger the proportional band, the slower the response
time of the weighfeeder. The smaller the proportional band, the more likely the weighfeeder is to go
unstable and begin to hunt up and down.
When the flowrate is this value above setpoint the PI Demand is -100%. When the flowrate is this
value below setpoint, the PI Demand is 100%. As the flowrate approaches setpoint, from above or
below, the PI Demand falls proportionally to 0% at setpoint.
However, these values assume that the Integral portion of the PI Control is adding 0% to PI demand.
If the Integral is adding 50%, then the PI demand is -50% one proportional band above setpoint,
50% at setpoint and 100% at half a proportional band below setpoint.
The PI Demand is limited to be within the range -100% to 100%. So in the above example, at one
proportional band below setpoint the PI Demand is still 100%(not 150% as might be expected). This
has been achieved by automatically forcing the Integral portion to 0%. Similarly, at two proportional
bands below setpoint the PI Demand is still 100%, achieved by automatically forcing the Integral
portion to -100%.
As a starting point, the ‘proportional band’ should be set to twice the flowrate achieved by the system
when the speed demand output is at 100%. If the weigh feeder is unstable (hunts), increase the
value. If the weigh feeder is slow to respond, decrease the value.
Q23712 integral time constant (increase for slow systems) 8462 3.2 s
This is the integral time constant. It sets the rate at which the integral control changes the PI demand
until the flowrate is correct. Note that the Integral action is disabled when the speed demand is 0%
and the flowrate is above the setpoint and also when the speed demand is 100% and the flowrate is
below setpoint.
Q23714 slew rate limit (limits rate of change to setpoint) 8466, g8 50 %/s
Limits the rate at which PI demand can change.
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