Recently, we had an interesting inquiry from a customer about having a VFD go to a preset speed from a single input. In this case, that would pre-empt the speed the drive is being commanded to in normal circumstances.
For example, when an exhaust fan ramps up typically by building pressure, while it really should go to full speed on a local command from a fire panel or other gas sensor.
In the example above, the VFD is utilizing jog mode, which can also be used in cases where the system has a single input that you want to use to start the motor AND go to a preset speed, with no other speed reference required.
What sets jog mode apart? This setting is different than other modes, such as fire mode, which simply ignores all alarms, and runs the VFD until it burns up. Sometimes, the sequence doesn’t need that, and so you can adjust to something a little simpler, such as jog mode. While jog mode still monitors the safeties and alarms from the VFD, plus, it will trip if limits are exceeded.
Once the drive has been started and is running smoothly, typical s/s signal on term 12/18 and speed ref on 53/55, users can add the “jog” signal to terminal 29, when utilizing the example share in this blog post. However, on some new drives terminal 29 may be defaulted to “jog” already, so make sure to take a look at your system to find what your VFD requires specifically.
Here are some additional steps to setting your VFD to jog mode:
Set 3-11 “jog speed” to the speed you want the vfd to run
Set 5-13 terminal 29 to [14] “jog”
At that point, a contact closure between 12/29 will put the drive into jog mode and run at the jog speed.
While we hope this is helpful, please feel free to reach out if you’re still stuck putting your VFD into jog mode, or if these steps didn’t work for your specific VFD system. Our AirReps team is always here and ready to help you with all things HVAC.