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Rotation numbers are displayed on the home screen in the Status Bar, as well as on the sequencing
diagnostics page.
5.4.2 How the ES+ Controls Pressure While Sequencing
Each compressor operates exactly the same as if it were in Automatic mode with one exception: it
has a dynamic setpoint. The initial setpoint is determined by the equation shown above. A
compressor starts when the system pressure drops below its programmed reset point, after waiting
for [Lag Start Interval * (rotation number - 1)] seconds. This prevents all lag compressors from
starting at once. Note that a compressor's timer is not reset to zero until that compressor is started
or until another unit in the system stops. This means that the time for the next lag compressor to
come on may be somewhat less than the programmed Lag Start Interval setting.
For example, consider a three compressor sequence system with the following settings, Target
Pressure = 100 PSI; Load Pressure = 90 PSI; Lag Start Interval = 15 seconds. The lead compressor
is running alone, maintaining 100 PSI by modulation when an air tool comes on line and causes the
air demand to exceed the capacity of the lead compressor. When the pressure drops to 90 PSI, the
#2 unit times out its 15 second timer and starts. It takes 5 additional seconds for the pressure to
rise above 90 PSI. The #3 unit whose timer was initially set at 30 seconds (15 x [3 - 1]), has counted
down 20 seconds (the total time that system pressure was below 90 PSI). If air demand increases
again, the pressure will have to fall below 90 PSI for only 10 seconds more to start unit #3.
A lag compressor's target setpoint is [Target Pressure - 3(rotation number - 1)]. So, in the above
example the first lag compressor (rotation #2) has a Target Pressure of 97 PSI; the second lag, 94
PSI, and so on. But look what happens in an eight compressor installation: The eighth compressor
will have an initial setpoint of [100 - 3(8 - 1)], or 79 PSI. However, this does this not mean that an
eight compressor installation must operate 21 PSI below the desired operating point when all
compressors are running. This is where the dynamic setpoint control takes over. Whenever the
system pressure is below the programmed Load Pressure, the Target Setpoint of each lag
compressor is incremented at a pre-determined rate. After a short interval (about five minutes in
this example), the Target Setpoint of the last sequenced compressor will climb until either it equals
the Load Pressure, or a decrease in demand causes the actual system pressure to rise above the
Load Pressure. The system will maintain delivery pressure between the Load and Target set points.
Dynamic setpoint control will also work in reverse of the operation described above. Obviously,
incrementing set points will cause overlap of the compressors' modulation ranges. While this
enables us to maintain a higher pressure, overlap is undesirable as demand decreases, because a
system could end up with several compressors running partially loaded instead of running the
minimum number of fully loaded compressors. To overcome this, as pressure rises through the
range between Load Pressure and Target Pressure, the lag compressors' Target Pressures are now
decremented. This reverses the effect described above during periods of high demand.
5.4.3 Automatic Sequence Change
A controller will be the Lead compressor for the time programmed as Transfer Interval. Then, it
assigns itself the highest available rotation number. The lag compressors detect this and decrement
their rotation numbers. Number 2 becomes number 1, the new lead; number 3 becomes number 2,
etc.
Whenever a missing rotation number is detected, such as when a compressor is turned off that was
previously in the rotation, it will automatically 'close the gap' by decrementing the rotation numbers
of all compressors whose rotation numbers were greater than the missing number. Likewise, if for
whatever reason the lead compressor fails to carry out its role, all lag compressors begin
decrementing their rotation number until a new lead is established. Regardless of the scenario, the
result will always be that the compressors that remain in rotation will end up with the lowest possible
rotation numbers.
Summary of Contents for Governor
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