Detect if 3-phase 110VAC motor is running via 24VDC PLC input
Such things exist. (It's very hard to come up with an original question these days.) For example, the Crouzet Current Monitoring Relay with SP-NO/NC Contacts, 24 → 240 V ac/dc.



Figure 1. A current sensing relay. See RS Online.

Specifications for this unit are:

Operating voltage:              24 V → 240 Vac / Vdc (-15% / +10%)
Measurement range:              2 → 20 A
continuous overload (°25@C):    100 A
Measured signal frequency:      40 → 70 Hz sinusoidal
Measurement cycle (max.):       30 msec / Measurement in true RMS
Threshold setting:              10 → 100% of the range
Response time:                  200 ms
Start delay:                    500 ms
Output:                         1 single changeover relay


The relay contact can be used to switch your PLC input.

A websearch for current monitoring relay will give you plenty of options.