Analog Current Sensor vs. Adjustable Digital Current Switch

Using a current sensor allows the user to measure the exact current drawn by the ECM. After installing the sensor as per the instructions. The BAS is scaled so that the monitored current range matches the analog output of the device (e.g. 0-10 Vdc = 0-100A.) In this way, the amperage drawn by the ECM can be measured.

Using an adjustable current switch allows the installer to set a trip point at a specific current level. First, determine the keep-alive current for the ECM (i.e., the current drawn when the motor is connected to the AC power source, but the shaft is not turning). Second, adjust the current switch so that he trip point is slightly higher than the keep-alive current. This way, the current switch will activate after the ECM starts running. Note that the GNG current switches are not appropriate for use in ECM applications.

In the example below, the keep-alive current for ECM used in the application is a 0.5A therefore, set the trip point of the current switch to 0.75A.

1. The ECM is drawing keep-alive power only. The motor is powered but the shaft isn’t turning.
2. When the shaft begins to turn the current increases past the trip point of the switch, and the status of the switch changes state.
3. The ECM is drawing a stable current during normal operation.
4. The ECM is experiencing mechanical problems and the current drops sharply.
5. The current switch changes status again as the monitored current drops below the trip point, sending an alert to the control system.
6. The ECM continues to draw keep-alive current, as it is no longer operating with the shaft not turning, as long as it remains connected to the AC power source.