Use of multiplexers

Multiplexers such as Campbell Scientific AM16/32B can connect up to 32 CS650 sensors to a single control or U terminal. When using multiplexers, the simplest configuration is for all sensors to have the same SDI-12 address.

When multiplexing CS650 sensors, use the switched 12V terminal so power to the sensor is turned off under program control before the multiplexer switches to the next terminal.

CAUTION:

Failure to turn off the switched 12 Volt terminal before clocking the multiplexer damages the multiplexer relays.

The proper sequence in the data logger program for measuring CS650 sensors on a multiplexer is:

  1. Set RES control port high to enable multiplexer

  2. Pulse CLK control port to advance to next multiplexer terminal

  3. Set switched 12 volt terminal high to supply power to CS650

  4. Delay for 3 seconds for sensor to warm up

  5. Send SDI-12 command(s) to CS650

  6. Set switched 12 volt terminal low to remove power from CS650

  7. Repeat steps 2 through 5 for each CS650 connected to the multiplexer

  8. Set RES control port low to disable multiplexer

Program examples in Example programs show the commands used in CRBasic.