Circuit to control heater elements in sapflux experiments.
To measure the rate of sap flow through trees using either the thermal disipation method or the pulse method a means of injecting heat into the sapwood is required. This is done by passing an electrical current through a resistive element embedded in the tree. Depending of which of the two methods is employed a continuous heat flow of 250mW or a pulse of around 10J is required. The power source is usually 12V, be it a mains powered power supply, a standalone battery, or a battery recharged from a photovoltaic system. In the last two scenarios the supplied voltage can vary by several voltages during charging or as the battery discharged.
We require a means of providing an adjustable, constant voltage to the heater probes, one that can be switched on and off by the datalogger in the measurement system.
The system needs to have some resilience to lightning strikes.
-
Input voltage range 12V to 15V DC
-
Output voltage adjustable from 15V down to 3V
-
Power disipation around 10W - depending on heatsink size
-
Maximum continue current 10A - depending on power dissipation
-
Maximum induced current from a 1/100us lightning pulse: 70A
-
Can be enabled with signal from 2V to 15V, disabled below 1V
-
Can be configured as a switch only
-
Can be configured to allow pulse width modulation (PWM) voltage level control (I.e. allow digital setting of the power level)
-
PCB size 1.5" by 2.5"
Developed using KiCAD (http://kicad-pcb.org/).
Inline-style:
