Menu 14 − User PID Controller

Mode: RFC‑A

PID controllers

PID Controller 1 is used by the Pump software as the main process PID. PID Controller 2 is an auxiliary PID and may be used to control external equipment if requred e.g. actuated proportional valves. Both operate in the same way except that PID controller 2 does not include a pre-sleep boost reference or alternative feedback and error selection. The sample rate for the PID controllers is 4ms.

PID1 is used as the main process PID controller by the Pump software.

Controller

The controller section for the PID controllers is shown in the introduction. The structure of PID controller 1 shown in the introduction is when PID1 Mode Selector (14.059) = 0, PID1 Feedback Output Scaling (14.058) = 1.000, and PID1 Feedback Square Root Enable 2 (14.062) = 0. The additional features provided by these parameters are not available for PID controller 2, and so this controller always has the structure shown. If the combined enable is inactive then all internal states are held at zero and the destination parameter will be defined by PID1 Feed-forwards Reference (14.019) alone. If the enable is active the PID controller is active even if the destination is not routed to a valid parameter or to 0.000. It should be noted that if either of the enable sources is routed to 0.000 or to a non-valid parameter the source value is taken as 1, therefore with default settings, PID1 Enable Source 1 (14.009) = 0.000 and PID1 Enable Source 2 (14.027) = 0.000, the PID controller can be enabled by simply setting PID1 Enable (14.008).

PID1 Error (14.022) is the difference between the reference and feedback produced by the reference and feedback systems described in the previous sections. The PID controller output is defined as follows:

PID1 Output (14.001) = PID1 Error (14.022) x [Kp + Ki/s + sKd/(0.064s + 1)]

Kp = PID1 Proportional Gain (14.010)

Ki = PID1 Integral Gain (14.011)

Kd = PID1 Differential Gain (14.012)

Therefore:

1. If PID1 Error (14.022) = 100.00% the proportional term gives a value of 100.00% if PID1 Proportional Gain (14.010) = 1.000.

2. If PID1 Error (14.022) = 100.00% the integral term gives a value that increases linearly by 100.00% per second if PID1 Integral Gain (14.011) = 1.000.

3. If PID1 Error (14.022) increases linearly by 100.00% per second the differential term gives a value of 100.00% if PID1 Differential Gain (14.012) = 1.000. (A filter with a time constant of 64ms is provided on the differential gain to reduce the noise produced by this term.)

The output may be limited to a range that is less than the maximum range of PID1 Output (14.001) using PID1 Output Upper Limit (14.013) and PID1 Output Lower Limit (14.014). If PID1 Output Lower Limit (14.014) > PID1 Output Upper Limit (14.013) then the output is held at the value defined by PID1 Output Upper Limit (14.013). If PID1 Symmetrical Limit Enable (14.018) = 1 then the lower limit = -(PID1 Output Upper Limit (14.013)). If the output reaches either of these limits the integral term accumulator is frozen until the output moves away from the limit to prevent integral wind-up. The integral hold function can also be enabled by the user by setting PID1 Integral Hold (14.017) = 1.

PID1 Output Scaling (14.015) can be used to scale the output, which is limited to a range from -100.00% to 100.00% after this function. The output is then added to PID1 Feed-forwards Reference (14.019) and is again limited to the range from -100.00% to 100.00% before being routed to the destination defined by PID1 Destination (14.016).

PID1 is used as the main process PID controller by the Pump software.

PID1 Feed-forwards Reference Source (14.002) is used to set the source parameter for PID1 feedforward reference source. It is not used by default by the Pump software but may be added if required.

See PID1 Digital Feed-forwards (14.073) and PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

PID1 Reference Source (14.003) is used to set the source parameter for PID1 reference source. By default, it is pointed at PID Final Setpoint Percent (29.030) so it is serviced by the Pump software. It is not recommended to change this.

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.

PID1 is used as the main process PID controller by the Pump software.

PID1 Feedback Source (14.004) is used to set the source parameter for PID1 feedback source. By default, it is pointed at PID Final Feedback Percent (29.035) so it is serviced by the Pump software. It is not recommended to change this.

The feedback sections are always active even if the PID controller itself is disabled or the reference sources are not routed to valid parameters. If a feedback source is not a valid parameter or is 0.000 then the value is taken as zero.

PID1 is used as the main process PID controller by the Pump software.

PID1 Reference Invert (14.005) may be used in combination with PID1 Feedback Invert (14.006) to invert the response characteristics of the main process PID. If PID1 Feedback Source (14.004) and PID1 Reference Invert (14.005) = Off(0) then the main process PID will give a normal error response characteristic. See the following diagram:

If PID1 Feedback Source (14.004) and PID1 Reference Invert (14.005) = On(1) then the main process PID will give an inverted error response characteristic. See the following diagram:

Note that the Wake Detect Feedback Threshold (29.049) changes function depending on how PID1 Feedback Source (14.004) and PID1 Reference Invert (14.005). See Wake Detect Feedback Threshold (29.049).

See PID1 Reference (14.020).

PID1 is used as the main process PID controller by the Pump software.

PID1 Reference Invert (14.005) may be used in combination with PID1 Feedback Invert (14.006) to invert the response characteristics of the main process PID. If PID1 Feedback Source (14.004) and PID1 Reference Invert (14.005) = Off(0) then the main process PID will give a normal error response characteristic. See the following diagram:

If PID1 Feedback Source (14.004) and PID1 Reference Invert (14.005) = On(1) then the main process PID will give an inverted error response characteristic. See the following diagram:

Note that the Wake Detect Feedback Threshold (29.049) changes function depending on how PID1 Feedback Source (14.004) and PID1 Reference Invert (14.005). See Wake Detect Feedback Threshold (29.049).

See PID1 Reference (14.020).

PID1 is used as the main process PID controller by the Pump software.

This introduces a fixed rate slew function that may be used to filter an incoming reference to the PID e.g. if the Pump software setpoint is derived from a noisy analog source such as a potentiometer.

See PID1 Reference Source (14.003).

PID1 is used as the main process PID controller by the Pump software. PID1 Enable (14.008) provides a means for the user to disable the main process PID for systems that don't require the motor speed to be controlled in order to reach a particular setpoint. A typical system is a pump that fills a tank, with a fixed head, where high level and low level switches are used to command the pump to start or stop, (see Level Switch Mode (29.082)).

When PID1 Enable (14.008) = On(1) and Auto is selected, Auto Select Input (29.015) = On(1), the main process PID output reference is selected, Auto Mode Reference (01.021).

When PID1 Enable (14.008) = Off(0) and Auto is selected the main process PID is disabled and the drive will run from the fixed speed reference set by PID Disabled / Feedback Loss Reference (01.023).

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

By default, this is directed to PID Software Enable (29.038) as required by Pump software to operate correctly. This allows the Pump software to control when the PID is enabled or disabled. The user can still manually disable the PID if required by setting PID1 Enable (14.008) to Off(0).

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

PID1 Differential Gain (14.012) is main process PID1 loop differential gain. The default value of 0.000 is a good starting point for most applications. Note that the differential gain gives an output proportional to the rate of change of error which for most systems only serves to amplify feedback noise, it is recommended to leave this at 0.000.

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software. 

PID1 Output Upper Limit (14.013) defines the PID output upper limit in percent units. It is written to by the Pump software and can’t be modified by the user.

If Dry Well Low Load Mode (29.059) = Lower PID Output and a dry well condition has been detected, PID1 Output Upper Limit (14.013) is set to Dry Well Low Load PID Output Reduction (29.060) .

For all other conditions PID1 Output Upper Limit (14.013) is set to 100.00%, as required by normal PID operation.

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software. 

PID1 Output Lower Limit (14.014) sets the minimum output for the main process PID, where the default of 0% is recommended such that reverse rotation of the pump is prevented, while running in Auto mode. 

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

PID1 Output Scaling (14.015) implements a PID output scaling function. It is recommended to leave this at the default of 1.000 for normal operation.

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

By default, this is directed to Auto Mode Reference (01.021) as required by Pump software to operate correctly in Auto mode.

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

PID1 Integral Hold (14.017) is used to prevent PID integral term from winding up in some applications. The default of Off(0) is suitable for most Pump applications.

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

When PID1 Symmetrical Limit Enable (14.018) = Off(0), PID1 Output Upper Limit (14.013) and PID1 Output Lower Limit (14.014) define the main process PID output limits.

When PID1 Symmetrical Limit Enable (14.018) = On(1), PID1 Output Upper Limit (14.013) defines the main process PID output limits where the lower limit = - ( PID1 Output Upper Limit (14.013) ).

The default of Off(0) is recommended such that reverse rotation of the pump is prevented, while running in Auto mode.

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

PID1 Feed-forwards Reference (14.019) indicates the level of the PID1 feed-forward reference, which is the sum of PID1 Feed-forwards Reference Source (14.002) and PID1 Digital Feed-forwards (14.073), in percent units.  

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump  software.

PID1 Reference (14.020) indicates the level of the PID1 reference, which is the sum of the parameter pointed to by PID1 Reference Source (14.003) and PID1 Digital Reference (14.025), multiplied by PID1 Reference Scaling (14.023), in percent units.

Reference

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).

PID1 is used as the main process PID controller by the Pump software.

PID1 Feedback (14.021) indicates the level of the PID1 feedback, which is the sum of the parameter pointed to by PID1 Feedback Source (14.004) and PID1 Digital Feedback (14.026), multiplied by PID1 Feedback Scaling (14.024), in percent units.

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 feedback 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.

PID1 is used as the main process PID controller by the Pump software.

PID1 Error (14.022) indicates the main process PID error in percent units.

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

PID1 Reference Scaling (14.023) implements a PID reference scaling function that is applied to the sum of the parameter pointed to by PID1 Reference Source (14.003) and PID1 Digital Reference (14.025). It is recommended to leave this at the default of 1.000 for normal operation.

See PID1 Reference (14.020).

PID1 is used as the main process PID controller by the Pump software.

PID1 Feedback Scaling (14.024) implements a PID reference scaling function that is applied to the sum of the parameter pointed to by PID1 Feedback Source (14.004) and PID1 Digital Feedback (14.026). It is recommended to leave this at the default of 1.000 for normal operation.

See PID1 Feedback (14.021).

PID1 is used as the main process PID controller by the Pump software.

PID1 Digital Reference (14.025) is summed with the value of the parameter pointed to by PID1 Reference Source (14.003), after conversion to a percentage of the parameter maximum, and passed to PID1 Reference Scaling (14.023). It may be used to provide an offset the value of the parameter pointed to by PID1 Reference Source (14.003).

For normal operation of the Pump software, it is recommended to leave PID1 Digital Reference (14.025) at the default of 0.00%.

See PID1 Reference (14.020).

PID1 is used as the main process PID controller by the Pump software.

PID1 Digital Feedback (14.026) is summed with the value of the parameter pointed to by PID1 Feedback Source (14.004), after conversion to a percentage of the parameter maximum, and passed to PID1 Feedback Scaling (14.024). It may be used to provide an offset to PID1 Feedback Source (14.004).

For normal operation of the Pump software, it is recommended to leave PID1 Digital Feedback (14.026) at the default of 0.00%.

See PID1 Feedback (14.021).

PID1 is used as the main process PID controller by the Pump software.

By default, this is directed to Drive Active (10.002) as required by Pump software to operate correctly. This ensures the PID is disabled if the drive is not active. The user can still manually disable the PID if required by setting PID1 Enable (14.008) to Off(0).

See PID1 Output (14.001).

PID1 is used as the main process PID controller by the Pump software.

PID1 Pre-sleep Boost Level (14.028) is used to provide a small amount of PID reference boost as the drive enters Sleep Detect Speed Threshold (29.051), as indicated by Sleep Required Output (29.053). The boost level is only applied for a maximum of PID1 Pre-Sleep Maximum Boost Time  (14.029) seconds.

This feature is a benefit in pumping systems where the output of the pump is controlled by a valve. In this scenario boosting the setpoint by a small amount can help prevent the system from going to sleep as often, and in the event that the system does go to sleep the boost in pump output will hold the system in sleep for longer reducing pump wear and running costs.

See PID1 Reference (14.020).

PID1 is used as the main process PID controller by the Pump software.

The PID1 Pre-sleep Boost Level (14.028) is only applied for a maximum of PID1 Pre-Sleep Maximum Boost Time  (14.029) seconds.

See PID1 Pre-sleep Boost Level (14.028).

See PID1 Output (14.001).

See PID1 Feed-forwards Reference Source (14.002).

See PID1 Reference Source (14.003).

See PID1 Feedback Source (14.004).

See PID1 Reference Invert (14.005).

See PID1 Feedback Invert (14.006).

See PID1 Reference Slew Rate (14.007).

See PID1 Enable (14.008).

See PID1 Enable Source 1 (14.009).

See PID1 Proportional Gain (14.010).

See PID1 Integral Gain (14.011).

See PID1 Differential Gain (14.012).

See PID1 Output Upper Limit (14.013).

See PID1 Output Lower Limit (14.014).

See PID1 Output Scaling (14.015).

See PID1 Destination (14.016).

See PID1 Integral Hold (14.017).

See PID1 Symmetrical Limit Enable (14.018).

PID2 Feed-forwards Reference (14.049) shows the sum of the feed-forwards source selected in PID2 Feed-forwards Reference Source (14.032) and PID2 Digital Feed-forwards (14.083).

See PID1 Reference (14.020).

See PID1 Feedback (14.021).

See PID1 Error (14.022).

See PID1 Reference Scaling (14.023).

See PID1 Feedback Scaling (14.024).

See PID1 Digital Reference (14.025).

See PID1 Digital Feedback (14.026).

See PID1 Enable Source 2 (14.027).

PID1 is used as the main process PID controller by the Pump software.

PID1 alternative feedback and error selection

The description given in PID1 Output (14.001) assumed that PID1 Mode Selector (14.059) = 0 so that PID controller 1 uses its own feedback (FBK1). It is possible to select alternative configurations that allow various combinations of feedback or error from either PID controller to be used as shown below.

PID1 Mode Selector (14.059) can be used to select the feedback and error as shown in the table below. It should be noted that PID controller 2 will operate normally even when its feedback or error has been selected for PID controller 1. However, if PID1 Mode Selector (14.059) is non-zero PID controller 2 enable is controlled directly by the enable state of PID controller 1.

PID1 Feedback Output Scaling (14.058) can then be used to scale the results. PID1 Feedback Square Root Enable 2 (14.062) can be used in converting the output of the combined feedback from pressure to flow. 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.

PID1 is used as the main process PID controller by the Pump software.

See PID1 Feedback Output Scaling (14.058).

PID1 is used as the main process PID controller by the Pump software.

PID1 Feedback Square Root Enable 1 (14.060) applies a square root function to PID1 Feedback (14.021), 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 flow as its reference and feedback and the motor is controlling a pump. 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.

See PID1 Feedback (14.021).

See PID1 Feedback Square Root Enable 1 (14.060)

PID1 is used as the main process PID controller by the Pump software.

PID1 Feedback Square Root Enable 2 (14.062) can be used in converting the output of the combined feedback from pressure to flow. 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.

See PID1 Feedback Output Scaling (14.058).

PID1 is used as the main process PID controller by the Pump software. 

PID1 Output With Feed-forwards (14.070) shows the output of the PID controller after the scaling in PID1 Output Scaling (14.015) has been applied, plus the contribution from the feed-forwards term.

PID1 Output With Feed-forwards (14.070) = PID1 Output (14.001) x PID1 Output Scaling (14.015) + PID1 Feed-forwards Reference (14.019)

PID1 is used as the main process PID controller by the Pump software. 

PID1 operates normally if this parameter is zero. If PID1 is enabled and this parameter is set to one PID1 Output (14.001) is forced to the level of PID1 Output Preset Level (14.072) subject to the limits defined by PID1 Output Upper Limit (14.013) and PID1 Output Lower Limit (14.014). To give a smooth transition when this parameter is subsequently set to zero, the integral accumulator is set to PID1 Output Preset Level (14.072) - PID1 Proportional Gain (14.010) x PID1 Error (14.022) and the differential term filter output is reset to zero.

PID1 is used as the main process PID controller by the Pump software. 

PID1 Output Preset Level (14.072) defines the level that the PID output will be preset to when PID1 Output Preset Enable (14.071). See PID1 Output Preset Enable (14.071).

PID1 is used as the main process PID controller by the Pump software. 

PID1 Digital Feed-forwards (14.073) allows the user to define a static PID feedforward value as percentage. See PID1 Feed-forwards Reference (14.019).

If the PID feed forward is set to 50%, when auto mode is active, the feed forward term will rapidly bring the pump motor up to 50% of  Maximum Reference Clamp (01.006). Most pumping applications only give an appreciable output when 50% of the motor rated frequency speed is reached. This reduces the control effort required from the PID controller I term, thereby reducing overshoot and control delay when Positive Minimum Reference Clamp (01.004) is set > 0. One way to configure this is to set PID1 Digital Feed-forwards (14.073) to 50%.

PID2 Output With Feed-forwards (14.080) shows the output of the PID controller after the scaling in PID2 Output Scaling (14.045) has been applied, plus the contribution from the feed-forwards term.

PID2 Output With Feed-forwards (14.080) = PID2 Output (14.031) x PID2 Output Scaling (14.045) + PID2 Feed-forwards Reference (14.049)

PID2 operates normally if this parameter is zero. If PID2 is enabled and this parameter is set to one PID2 Output (14.031) is forced to the level of PID2 Output Preset Level (14.082) subject to the limits defined by PID2 Output Upper Limit (14.043) and PID2 Output Lower Limit (14.044). To give a smooth transition when this parameter is subsequently set to zero, the integral accumulator is set to PID2 Output Preset Level (14.082) - PID2 Proportional Gain (14.040) x PID2 Error (14.052) and the differential term filter output is reset to zero.

See PID2 Output Preset Enable (14.081).

See PID2 Feed-forwards Reference (14.049).