In our energy conscious world, measurement of the performance of our equipment is becoming more necessary. Sub-meters are being installed throughout our buildings to monitor more closely where the energy we buy is actually consumed. As energy monitoring becomes more important, we should all consider buying, specifying, and using analog current transducers, also called current analog sensors, to connect equipment to our control systems. The digital types, also called current switches, perform their purpose simply and effectively, but the analog type has the advantage to add many more functions and capabilities and is usually less expensive!
To name just a few advantages:
The current used by the equipment can be trended in an analog style instead of a digital (on/off) style. These trends can establish a baseline to use as historical comparisons or to observe operating characteristics not usually seen about the equipment. Some of these things include: dirty filters, low water, bearing problems, and more.
Related to the above description on trending is the ability of the control system to set alarms for different current levels detected. Schneider Electric’s StruxureWare software makes creating and managing these alarms easy and powerful. Several alarms can be set on one piece of equipment.
A good rule of thumb for a motor is that if it is running without a load, it will usually pull about 1/3 of the full load current indicated on the nameplate of the motor. If the nameplate shows a full load amperage of 10 amps for the motor, it will likely draw 1/3 of that amount or 3.3 amps if the motor is running unloaded. This information is useful because if our equipment happens to break a fan belt or a pump coupling, the motor will essentially be running unloaded. We can now set alarms to help us to monitor the condition of our equipment.
Analog CT’s can give us a great picture of the energy consumed in our facilities. By multiplying the current measured by the voltage of the motor and the three-phase correction factor as required we can determine the kilo-watts (actually the kVA) used by the motor.