Campbell Scientific CS700 Tipping Bucket Rain Gage and CS700H Heated Rain Gage - Manual (Page 31)

Appendix A. CS700H Operation
When snow is last detected, a timer is left running, to keep the heater cycling
so that any snow built up on the funnel will be melted. This “Snow Run-on”
timer is factory preset to 18 minutes but may be extended as required.
The heater will cycle on and off for this “Run-on” time OR while ever snow is
detected (see Figure A-3).
FIGURE A-3. Diagram showing how the “Snow Run-On” timer
controls the heater.
A.1 High Power Operation
If the snow sensor is disabled (X22 command set to 0), the heater will cycle
continually when the ambient temperature falls below the “Active On”
temperature (X23 command) and is above the Low Off Temperature (X25
command). This assumes the system is active. Because this mode consumes
more power, high power operation is only recommended when the CS700H
uses AC power.
A.2 External Control
The CS700H is set to by default to Automatic control – where the CS700H
monitors the ambient temperature and the snow sensor and operates the heater
automatically. Dataloggers in weather stations that monitor the ambient
temperature and the snowfall can control the tipping bucket heaters directly.
Simply set the X20 command to 1 for External Control, and then use the X29
command to enable the heaters to cycle on/off (=1) or disable the cycling (=0).
The ambient temperature, block temperature, snow sensor and state of the
heaters can be measured using the M, R or the C command, as normal.
The Setpoint Temperature is the required temperature of the
funnel – and not the block temperature read from M and the R
command. The relationship between the funnel temperature,
block temperature and ambient temperature has been determined
through extensive testing. NOTE
There is an alternate external control mode, whereby the controlling system
can actually turn the heating elements on and off. This is done using the X21
command, with heater “on” (=1) and heater “off” (=0).
If the heating elements are left turned on, the funnel
temperature may reach a point where the snow evaporates
before it hits the funnel! CAUTION
A-3