The OTT Pluvio
2
S unit heats the orifice rim until the target temperature of +4 °C
(factory setting) is reached – as far as heating power and ambient conditions
a
llow. To achieve this, the heater control system measures both ambient and ori-
fice rim temperatures and uses these values together with the target temperature to
calculate the pulse/pause ratio. Depending on this value, the heater control system
supplies electricity to the heating element for 5 to 120 seconds.
In addition to this, several modes of operation provide the option of enabling/
disabling the heater control system based on certain criteria (see below).
When the heater control system is enabled, the OTT Pluvio
2
S unit continuously
performs a functional test for the orifice rim heater (heater self-test) to detect
p
otential error conditions. When the heater control system is temporarily disabled,
performing the heater self-test depends on the mode of operation set. The result is
used for system checks in the measuring area. In case the error cannot be correct-
ed (unusual operating conditions or faulty orifice rim heater), the "Heater function-
al check failed" status information is shown, refer to the response to the SDI-12
command aD2!, Chapter 6.1.
When the measured rim temperature exceeds 50 °C in heating mode, the rim
heater system triggers an automatic safety shutoff of the heating element.
The orifice rim heater can be switched ON/OFF using an advanced SDI-12 com-
mand or via a separate power supply. Thus, the orifice rim heater may completely
be switched OFF, for example in summer. In such case, a message is shown in the
Status Information (response to the SDI-12 command aD2!; value 8).
The nominal supply voltage for operating the orifice rim heater is 24 V
DC
, and the
maximum heating capacity with very low ambient temperatures is approx. 50
Watt. Optionally, the supply voltage of the orifice rim heater can be fed separate-
ly from or together with the supply voltage for the precipitation gauge.
As a special option, the orifice rim heater may be operated based on 12 V
DC
. In
this case, effective heating power is 25 % of the rated power. For operation in
moderate climate zones and using 12 V solar systems, this type of operation is
basically allowed. The data specified for 24 V
DC
operation cannot be maintained
across the entire temperature range (refer to Chapter 10, „Technical Data”). For
temperatures below –5 … –10 °C, snow or ice may adhere to the unit.
Orifice rim heater modes of operation:
䊳
Mode #0 Orifice rim heater is completely switched OFF.
(No heater self-test is performed).
䊳
Mode #1 Heater control system is continuously enabled.
The heater control system keeps the temperature of the orifice
rim at the preset target temperature.
(Factory setting)
䊳
Mode #2 Within a specified temperature range, the heater control system
is continuously enabled.
Same as Mode #1 with the heater control system temporarily
disabling the heater when the temperature is below an adjustable
temperature limit (–40 … +9 °C). Below the temperature limit, the
heater self-test is performed based on a selectable interval
(1 h … 7 d).
13
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