EMS 81 is the most recent version of sap flow system based on a tissue heat balance (THB) method. Since 1973 when it was established, the instrumentation was seriously upgraded and theoretical background was developed and verified. The biggest advantage of this approach is direct heating of relatively large volume of xylem which brings high accuracy of the sap flow estimation. The measuring unit is quite sophisticated and therefore also expensive but the underlying theory is clear, without any uncertain empirical parameters (Tatarinov et al. 2005) and without any need for field calibration. Latest system EMS 81 enables connection of the sensor for continuous measurement of stem increment. This additional device synergistically increases the value of measured data (i.e. indirect estimation of the stem water potential, calculation of water use efficiency). Measuring system consists of the MicroSet 8X controlling unit, sap flow sensor SF 81, set of stainless electrodes, weather shields and connecting cables.

Technical Details:

•  Channels 
  12 (for small stems or shoots)
•  Sensor diameters 
  8-12 mm and 12-18 mm (?2 mm allowed)
•  Heating technique 
  external soft and flexible heater
•  Output variable 
  sap flow in [kg/hr]
•  Temperature sensors 
  Special Thermocouple
•  Temperature difference 
  4?C, controlled
•  Resistance of heaters 
  100 Ohm
•  Heating current 
  maximum 0.125 A per channel
•  Heating power 
  maximum 1.6 W variable according to sap flow magnitude

Built-in datalogger Details:

•  Accuracy 
  0.3% of the full scale
•  Memory capacity 
  512 KB
•  Memory capacity 
  220,000 values (> three months of measurement)
•  Measuring interval 
  10 sec to 2 minutes
•  Storage interval 
  10 sec to 1 hour

Other Details:

•  Energy supply 
  12 V D.C. lead acid battery or DC power adapter
•  Current consumption 
  max 2.2 A (Generally, the power consumption is proportional to sap flow rate and the number of channels in use. Daily average of 0.2 to 0.5 A is supposed.)
•  Working temperature 
  -10 to 40 ?C
•  Weight 
  8 kg box, 12 kg cables, 2 kg sensors and accessories
•  Box size 
  43 x 33 x 20 cm