Decagon Em50 logger

Request Quote

The Em50 automatically recognizes the Drain Gauge and keeps a running total of drainage since the last time the data logger memory was erased. The Em50 will output the cumulative drainage in units of 0.1mm. For example, if the Drain Gauge has experienced 7 siphon flushes and the siphon chamber is half full at the time of measurement storage, the output would be 75, indicating 7.5 mm of drainage. The total drainage will not reset to zero when data are downloaded from the Em50, so the drainage reported is the cumulative amount since the Em50 memory was last erased. The Em50 will also output the water depth sensor mV reading at each wake interval.

Drain Gauge Interface

Request Quote | Specification Sheet

GEE Passive Capillary Lysimeter

The Drain Gauge is designed with a flush volume of 31 cm³ ±10%. If the sampling area is taken as the surface area of the opening in the DCT (divergence control tube) which equates to 310 cm², each flush event corresponds to 1 mm of drainage depth over the area of the DCT.

The lysimeter interface has been set to a maximum flow rate capability of 0.1 mm/minute or 144 mm/day. This is more than adequate for normal conditions.

If the device is not being used as a normal lysimeter, but is instead being used to measure run-off, the Smart Interface software can be rewritten to handle the much faster flow rates. If this has not been done, errors will occur. Errors will start to occur if the flow rate exceeds 0.3 mm/minute and once the flow rates exceed 0.5 mm/minute the results will be virtually meaningless.

Under normal lysimeter usage, the lysimeter will count the total flow up to 4999.9 mm. At this point, the next 0.1 mm will cause the count to reset to 0.0 mm. Therefore the total flow will always be:
          total flow = N × 5000 + the current reading in mm
where N is the number of resets. Reset events are not recorded in the device but they are evident from the logged results. 5000 mm is a massive amount and therefore reset events will be very rare. It may take years for a reset event to occur.

Testing the device

The device can only be tested by simulating 0.1 mm/minute (3.1 cm³) or less. This means for example just one small drip every 10 seconds. The device can then be logged over many hours to check the operation. The drip stream should be captured for a known time period and weighed to calculate the flow rate taking into account the Drain Gauge aperture. Pouring a quantity of water into the device will give a completely false result.

The interface checks the water level as mV output from the water depth sensor in the siphon tube every 1 minute. Then a 3.1 cm³ volume of water added to the clear calibration tube will show as an accumulation of 0.1 mm drainage on the datalogger.

Addition of water faster than 31 cm³ every 10 minutes will cause an error. Water will not be counted. Water should be added slowly and evenly at a rate of less than 31 cm³ per 10 minutes and if the datalogger is set to log every 60 seconds the accumulation of 0.1 mm or less of drainage depth, will be recorded by the datalogger each minute and 1 mm or less each 10 minutes.

For example, if the datalogger has an accumulation of 173.4 mm addition of 3.1 cm³ will result in 173.5 mm. If the datalogger has an accumulation of 173.9 and then 3 × 3.1 cm³ are added over each minute for 3 minutes, then the datalogger will show an accumulation of 174.2. The Drain Gauge will have syphoned after the first 3.1 cm³ and the additional 2 × 3.1 cm³ will record as 174.2.

Important Considerations

• The Drain Gauge sensor is intended only for use with data loggers and readout devices which can provide short excitation pulses. Continuous excitation not only wastes battery power, but may, under certain circumstances, cause the sensor to exceed government specified limits on electromagnetic emissions.
• If the data logger is programmed to wait too long between readings, it may miss a flushing event.