A click plc is nice and cheap and could.do.it. Free software too.
You.would have to calculate and test the proper setting points as well to trigger the relay. There are some devices other there though too. Let me dig one up
Search for a “set point relay”. That’s what they do, you create a set point on the range of the analog signal st which you want the relay to change state.
Advantech WISE-4060. Configured over web browser and can be used either online or offline. Outputs can be configured to do a number of things, one of them being an alarm output based on one of the analog inputs.