The reference section for the PID controllers is shown in the introduction. The pre-sleep boost control is only included in PID controller 1. The reference

sections are always active even if the PID controller itself is disabled or the reference sources are not routed to valid parameters. If a reference source

is not a valid parameter or is 0.000 then the value is taken as zero.

The reference is the sum of the reference source, the PID1 Digital Reference (14.025) and the PID1 Pre-sleep Boost Level (14.028) when it is active.

The result is multiplied by PID1 Reference Scaling (14.023) and then limited to +/-100.00%. The reference can then be inverted if required

(PID1 Reference Invert (14.005) = 1) and then a slew rate limit is applied with PID1 Reference Slew Rate (14.007). This limits the maximum rate of

change so that a change from 0.00 to 100.00% takes the time given in PID1 Reference Slew Rate (14.007).

Sleep mode is used to stop the motor if the frequency or speed reference falls below a specified level so that the system does not run inefficiently at low

speeds (see Sleep / Wake Threshold (06.053)). If the frequency or speed reference is controlled by PID controller 1 then the PID controller feedback will

fall when sleep mode becomes active because the motor has stopped. The PID controller output will rise again above the sleep/wake threshold and the

motor will restart. To minimise the number of transitions into and out of sleep mode the sleep condition can be delayed and an increased reference

applied during this period by setting PID1 Pre-sleep Boost Level (14.028) to a non-zero value. When Sleep Required (06.056) = 1 the PID1 Pre-

sleep Boost Level (14.028) is added to the reference until PID1 Error (14.022) is reduced below zero or until this additional reference has been applied

for PID1 Maximum Boost Time (14.029). This system is only intended for applications where PID controller 1 alone is used to control the motor

frequency or speed via the Menu 1 reference system and the motor rotates in the positive direction under normal conditions. When the PID output first

falls below the Sleep / Wake Threshold (06.053) it is possible for PID1 Error (14.022) to be negative because of a positive value remaining in the

integral accumulator. To allow the error to become positive so that the boost period is not terminated immediately, the PID1 Pre-sleep Boost Level

(14.028) is applied for a minimum of 100ms before the end of the boost period can be terminated because PID1 Error (14.022) is greater than or equal

to zero.

Parameter

14.004 PID1 Feedback Source

Short description

Defines the input source for the feedback for PID1

Mode

Open‑Loop

Minimum

0.000

Default

0.000

Type

16 Bit User Save

Display Format

Standard

Coding

RW, PT, BU

Feedback

The feedback section for the PID controllers is shown in the introduction. The feedback sections are always active even if the PID controller itself is

disabled or the feedback sources are not routed to valid parameters. If a reference source is not a valid parameter or is 0.000 then the value is taken as

zero.

The feedback is the sum of the feedback source and the PID1 Digital Feedback (14.026). The result is multiplied by PID1 Feedback Scaling (14.024)

and then limited to +/-100.00%. A square root function can be applied (PID1 Feedback Square Root Enable 1 (14.060) = 1) and the feedback can then

be inverted if required (PID1 Feedback Invert (14.006) = 1). The square root function is defined as follows.

Square root function output = Sign(Input) x 100.00% x √(|Input| / 100.00%)

where Sign(Input) = 1 if Input ≥ 0 or -1 otherwise

The square root function is useful in applications where the PID controller is operating with air flow as its reference and feedback and the motor is

controlling a fan. It is easier to use a pressure transducer than a flow transducer, and so the feedback from the transducer needs to be converted from

pressure to flow. As flow = Constant x √Pressure the square root function can be used in the conversion.

234

Maximum

59.999

Units

Update Rate

Drive reset read

Decimal Places

Maximum

59.999

Units

Update Rate