Frequency Source Switching when using Constant Pressure Setup
Requirement:
A Constant Water Pressure Setup solution is required for a VSD with Water Pump, but for maintenance purposes it is required, on an ad hoc basis, to override the Constant Water Pressure Setup and run the motor at a predefined speed (irrespective of pressure).
Solution:
VSDs offer a Frequency Source Switchover function which can be used to alternate between 2 different Frequency Sources. Unfortunately, the built-in PID Setting Source option Pressure Mode (C0-00=7) cannot be used as a Switchover option due to clashes in logic when used in combination with other Frequency Sources. As an alternative one can however use the PID feature in a somewhat different way to overcome these problems. This requires different settings than the usual Constant Water Pressure settings and the double line display (Keypad) will not display the feedback pressure on the top keypad display line (will display the running Amps which is the default for VSDs). The display parameter (b9-11) can however be changed to rather display the PID Feedback (b9-11=16) value, which will help to provide an indication of what the feedback pressure is, but will require adjusting C0-05 (PID Feedback Range) to adjust the range to display it as according to the applicable pressure value. Please see: https://www.emheater.co.za/faq/faq-keypad-display/
To set this up, please follow the wiring and parameter suggestions as follows:
Wiring:
- PID: Connect PID between +24V and AI2 and bridge GND and COM
- Frequency Source Switch: Connect a Switch between DI3 and COM to be used to switch between Frequency Source X and Frequency Source Y
- ON/OFF Switch: “If Required” – connect an On/Off Switch between DI1 and COM (and set b0-02=1)
Parameter Settings:
- Set b0-03 = 8 (Main Frequency Source X = PID)
- Set b0-04 = 6 (Auxiliary Frequency Source Y = Multi-Function)
- Set b0-07 = 02 (Frequency Source Logic Selection = Switchover between X and Y)
- Set b3-02 = 15 (DI3 = Frequency Source Switchover)
- Set C0-00 = 0 (PID Setting Source = C0-01)
- Set C0-03 = 1 (PID Feedback Source = AI2)
- Set b5-12 = 2 and b5-14 = 10 (to align with a 4-20mA feedback range)
- Set C0-01 = Set desired Target Pressure (Target Pressure as % of PID Feedback Range)
- Set b2-26 = Set desired WakeUp Frequency (must be set before setting b2-24)
- Set b2-27 = Set desired WakeUp Delay Time
- Set b2-24 = Set desired Sleep Frequency (must be set after setting b2-26 since it must be smaller than b2-26)
- Set b2-25 = Set desired Sleep Delay Time
- Set C1-00 = Set desired frequency to be used after switching to Frequency Source Y (as a % of the Maximum Frequency as set by b0-13)
