GHM Delta OHM HD2013.3, Operating Manual

Page: 9 / 26

HD2013.3
- 9 -
V1.2
4 CONFIGURATION AND MEASUREMENT
The configuration of the instrument and the reading of the measurements can be done
via the RS485 serial output, both with the proprietary protocol and with the MODBUS-
RTU protocol.
In the first 10 seconds after the instrument power on, it is always active the proprie-
tary protocol. After 10 seconds from power on, the operating protocol is activated,
which by default is the MODBUS-RTU protocol.
It is possible to keep the proprietary protocol active even after 10 seconds from power on
by sending, before the 10 seconds expire, the command
@ of the proprietary protocol.
The proprietary protocol can be set as operating protocol by means of the CP0 command.
The commands of the proprietary protocol and the registers of the MODBUS-RTU pro-
tocol are described in detail in the following chapters.
Precipitation measurement:
To determine if a precipitation is in progress, the instrument detects the percentage of
dry sensitive surface of the sensor:
100% = sensitive surface of the sensor completely dry
0% = sensitive surface of the sensor completely wet
When the percentage of dry sensitive surface of the sensor falls below a configurable
threshold value (default 95%), the instrument indicates that a precipitation is in
progress. The threshold value can be modified with the command CRTnn of the
proprietary protocol or by using the holding register with address 5 of the MODBUS-
RTU protocol.
The indication of precipitation in progress ceases when the percentage of dry sensitive
surface of the sensor rises above the threshold plus a configurable hysteresis value
(default 2%) and after a configurable delay time (default 2 minutes).
The resolution with which the percentage of dry sensitive surface of the sensor is
detected is 1% by default. The resolution can be set to 0.1% with the command
CRLRn of the proprietary protocol or by using the holding register with address 16 of
the MODBUS-RTU protocol.
The instrument discriminates between rainfall and snowfall based on the measured
ambient temperature. If the ambient temperature is lower than a configurable
reference temperature (default 2 °C), the precipitation is considered snowy.
Automatic calibration of the precipitation sensor:
The instrument can be set so as the precipitation sensor
calibration is automatically
performed at regular intervals; this allows compensating for any drift of the sensor
due to temperature changes, aging and dirt deposited on the sensitive surface.
The correction applied by each automatic calibration is limited to a maximum value
(configurable), so as to avoid erroneous calibrations when the detected value differs too
much from the estimated value.
By default, the automatic calibration is enabled, with 30 minutes interval and 0.1%
maximum correction. In order to change the automatic calibration settings, see the
chapters on the proprietary protocol and MODBUS-RTU protocol.