255-100 Novalynx
Analogue Output Evaporation Gauge
10
FIGURE 7-1. Multiplier and Offset Calculation Example
In this example, the pan is filled to a depth of 2 inches and the datalogger
reads 100 mV on the ga
u
ge. The pan is then filled to a depth of 8 inches and
the datalogger reads 2100 mV. This provides data for a two point calibration
).
Therefore the multiplier is:
m = (8 in – 2 in) / (2100 mV – 100 mV) = 0.003 in/m
V
The offset is:
b = 2 in – (0.003 in/mV • 100 mV) = 1.7 in
7.2 Automatically Refilling the Evaporation Pan
A simple solution for automatic refilling of the evaporation pan is provided by
the 255-620A Evaporation Pan Automatic Refill System. The 255-620A
consists of an electronic water timer powered by 2 AAA batteries and an
automatic float valve. The 255-620A must be connected to a user-provided
water supply. The water supply can be a pressurized system or a storage tank
that sits higher than the evaporation pan. The automatic float valve will stop
tank filling between 21.6 cm (8.5 in) and 24.1 cm (9.5 in), depending on water
pressure. The electronic water timer will enable tank filling at a user-set time
and interval.
If more precise fill control is wanted, program the datalogger to control a
solenoid valve in a fill line that’s connected to a water supply. A second
solenoid may be used for draining the pan in areas of high rainfall. Power
requirements need to be taken into consideration when using a solenoid valve.
