In this technical HVAC blog post, our VFD expert, Tom Mahrer provides the step-by-step process needed to provide a “Proof of Operation” via the VFD Relay to show that the motor is operating with a desired range of motor Amperage. The goal of this process is to generate a drive alarm if the remote disconnect at the fan is opened, and the solution is setting up current monitoring programming and applying it to a relay output.
To begin, our team used the Comparators function in the Smart Logic menu to compare drive motor current to a fixed value. We can then use a Logic Rule to combine both Comparators together and apply them to a Relay Output when the drive is commanded to run.
- Using the Main Menu, scroll down to the 13-** Smart Logic menu
- Select 13-1* Comparators
- Select Comparators 0
- Set 13-10 Comparator Operand to [4] Motor Current
- Set 13-11 Comparator Operator to [0] < Less than
- Set 13-12 Comparator Value to the high current limit. This was set to 19.
- Now select back and then select setup Comparators 1
- Set 13-10 Comparator Operand to [4] Motor Current
- Set 13-11 Comparator Operator to [2] > Greater than
- Set 13-12 Comparator Value to the low current limit. This was set to 1.
- Now go back to the 13-** Smart Logic menu and select 13-4* Logic Rules
- Select Logic Rules 0
- Set 13-40 Logic Rule Boolean 1 to [22] Comparator 0
- Set 13-41 Logic Rule Operator 1 to [1] AND
- Set 13-42 Logic Rule Boolean 2 to [23] Comparator 1
- Set 13-43 Logic Rule Operator 2 to [1] AND
- Set 13-44 Logic Rule Boolean to [33] Digital Input 18
- Now go to the 5-** Digital In/Out menu
- Select 5-4* Relays
- Select Relay 2
- Set 5-40 Function Relay to [70] Logic Rule 0
Relay output 2 will now close when the motor current is above 1 Amp and Below 19 Amps, and the drive is commanded to run. During operation if the motor current draw falls below 1 Amp or increases past 19 Amps the Relay 2 will open.
As always, please reach out to AirReps at [email protected] with any further questions or issues with your HVAC system today!