How to check the current in a sleeping H21 logger

            The purpose of this test is to check the current in a sleeping logger in order to pinpoint the cause of an unusually large power drain.  A circuit will be set up using a digital multimeter (DMM) to display the current.  By noting the increase in current when a new sensor is added to the logger, it is possible to determine which sensor is causing the problem.  This procedure assumes you have the double-ended battery cable, DMM and hook leads supplied by Onset, but alternative materials can be used.    

MATERIALS

1 9-V Battery

1 Double-ended 9-V Battery Cable

1 Digital Multimeter (DMM) with Hook Test Leads

1 Weather Station

1 PC with Boxcar Pro installed

1 Serial Cable

An assortment of sensors

PROCEDURE

Verify that the logger and battery are functioning:

1. Plug the 9-V battery directly into the Weather Station and remove any other batteries from the logger.
2. Attach the Weather Station to the PC using the serial cable.
3. Open Boxcar and launch the Weather Station.  Plug in all the sensors and verify that these sensors are listed in the “Sensor Information” section.  Check that the values displayed are reasonable.
4. Press Cancel to abort the launch.

Set up the circuit (see circuit diagram and picture on the next page):

5. Remove the 9-V battery from the Weather Station.  Plug one end of the battery cable into the Weather Station and the other end into the 9-V battery.  
6. Set the DMM to measure DC current at the 20 mA setting.
7. The black DMM cable should plug into the COM socket and the red cable should plug into the mA or A socket.
8. There are two open ends on the battery cable.  Clip the red lead of the DMM to the wire running to the logger, and the black lead of the DMM to the other wire that runs to the battery.  If you get this backward, the DMM will display a negative current, but otherwise everything will work fine.
9. With the circuit complete, the logger should be powered again.  Enter the launch screen with Boxcar to verify that everything is working.
10. Then press Cancel, unplug the serial cable from the logger and wait at least 60 seconds for the logger to go into sleep mode. 

Checking the current:

11. Check the reading on the DMM (you may need to adjust the range on the DMM to the 2mA scale).  This value represents the current drain when the logger is sleeping with all the sensors connected.  It should be less than 0.150 mA.  If it is not, then there is a problem with a sensor or the logger itself.
12. Use the process of elimination to find out what is draining excess current. Try un-plugging some sensors and note their effects on the current.  Most sensors should have a minimal impact (roughly 0.001 mA), while the wind sensors typical consume 0.010 to 0.020 mA.  If any one sensor consumes more than about 0.030 mA, then there may be a problem with that sensor.  If the logger consumes more than 0.010 to 0.030 mA then there may be a problem with the logger.