This manual is valid for instruments with firmware version 3.x or higher. Changes in the last
character of the ver sion number reflec t minor changes in the intern al software of the inst rument
that do not affect the manner in which the instrument should be operated.
The HygroLog HL20 data logger can record up to 20,000 pairs of relative humidity and temperature
values within the range of 0 to 100 %RH and -10 to 60°C (14 to 140°F).
The HygroLog HL21 data logger can record up to 20,000 tem perature valu es within the range of
-10 to 60°C (14 to 140°F). Models with the optional LC display are limited 0 to 50°C (32 to 122°F).
Temperature is m easured with a Pt100 RT D. Relative humidity is meas ured with a ROTRONIC
Hygromer IN1 capacitive sensor. Both sensors are internal and there is no apparent probe.
Both the HL20 and H L21 requ ire t hree A A ba tteri es (1.5V) for po wer. Depend ing o n bot h the log
interval and the display option, these dat a logger s can r ecord data o ver a t ime period of up to 2 0
months without replacing the batteries.
Configuration of the HL 20 and HL21, as well as the downloading and viewing of rec orded data,
requires a PC with the RO TRONIC HW4 software inst all ed as well as a s er vic e cable such as the
AC3006
Based on the ROT RONIC AirC hip 30 00 digital techno logy the HL20 an d HL21 of fer the f ollowing
features:
o Unit system: metric or English
o Real time clock (runs for up to 4 hours without the 3 AA batteries after initial charge)
o Calculation of the dew or frost point (calculated parameter can be displayed but not recorded)
o Optional LC display (%RH, temperature) with battery charge indicator and message bar
o Function key: starts and stops data logging, turns optional LC display on and off
o Status indicator ( LED): flashes gr een when logg ing, flashes r ed for out-of-limit valu es or a
logger problem
o Humidity temperature calibration and adjustment
o Simulator mode (used to validate the data recording function)
Note:
Instructions for using t he HW4 software are not incl uded in this manual. These instruc tions are
shipped separately on the software CD ROM.
All models ship wit h thr ee AA batt eries which must be inserted first (see battery replacement).
Note:
To conserve battery power, models with the LC display are shipped with the Display Sleep function
enabled and set to 1 minute (see Software Functions). When the function key has not been pressed
for some time (in this case 1 minute), the display sleep function automatically turns the display off.
The display can be temporarily turned on at any time by pressing on the func ti on key.
2.3.1 Battery lifetime
The battery lifetime depends on the manner in which the HL20 or HL21 is being used. The following
examples are based on the following assumptions:
o Fresh set of AA batteries (2900 mAh)
o Display backlight turned off (if applicable)
o Log interval set to 30 minutes
Battery lifetime in months
Models w/o LC display 20
Models with LC display, display sleep function set to 1 minute 13
Models with LC display, display sleep function disabled 5
2.4 Real time clock
After inserting a fresh set of batteries for the first time, the real time clock must be adjusted prior to
using the HL20 or HL21 ( see “Operation”) . The real tim e clock is powered f rom a large c apacitor
and can run for up to 4 hours without the batteries. Removing the battery for an extended period of
time will cause the logger to completely lose track of the date and time.
Because of the requirement to always keep track of the date an d time, the HL20 and HL21 do not
have a power on/off switch.
All models use a non-volatile EEPROM internal memory to hold the measurement data. The
memory cannot be removed from the data logger.
Memory capacity is as follows:
HL20: 20,000 pairs of relative humidity and temperature values
HL21: 20,000 temperature values
2.6 Function key
The function key is used as follows:
o Long key press: press the key for a few seconds to start or stop data logging.
o Short key press: depending on the configuration settings of the display (display sleep
function) a short key press turns on and off the optional LC display.
For more details, see “Operation”
2.7 Status indicator (LED)
The status indicator consist s of a green and red L ED. The green side of the LE D f lashes every 5
seconds when logging is active. The red side of the LED flashes every 5 seconds when a measured
value is out of limits (see “Configurable settings”) or when the logger requires attent ion (l ow batte ry,
memory full, major sensor failure – such as open or shorted sensor)
2.8 Service and data connector
The service / data connector (mini-USB type) can be accessed after removing the back cover (see
Operation). The connector gives access to the data logger UART digital interface (Universal
Asynchronous Receiver Transmitter).
Configuring the data logg er or retrieving the record ed data requires cab le AC3006 or equiv alent.
One end of the c able pl ugs into the ser vice / data connector. T he other end plu g s int o t he U SB of
a PC with the ROTRONIC HW4 software installed. See “Initial start-up” for the location of the
service / data connector.
Configuration of the data logger by the user and acc ess to its functions require s a PC with the
ROTRONIC HW 4 software (version 2.4.0 or h igher) installed. Service ca ble AC3006 is us ed to
connect the service / data connector to a USB port of the PC.
Instructions regarding the configuration of the data logger and access to its functions are provided
in the following manuals:
2.11.1 Relative humidity symbol and temperature unit
Both the symbol representing relative humidity and the temperature can be configured to suit local
requirements.
2.11.2 Calculated parameter
HL20: the data logger can be set to compute one of the following psychrometric parameters.
o Dew point (Dp)
o Frost point (Fp)
Note:
o When the optional display is configured to show the calculated parameter, either the symbol
Dp or the symbol Fp appear to the left of the numerical value, depending on whether the dew
point or frost point was selected. For values below freezing, the symbol Fp indicates that the
value is a frost point (above ice) as opposed to being a dew point (above liq uid) .
o The data logger cannot be used to record either the dew point or the frost point
2.11.3 Alarm function (out-of-limit value)
The alarm function can be enabled or disabled for each of the measured or calculated parameters.
High and low value can be associated with each p ara m eter so as to def ine out-of-lim its valu es. A
hysteresis value can also be entered for each parameter. The hysteresis value is used for both the
low and the high alarm conditions.
The data logger has a red LED which flashes when the value of any parameter is out-of-limits. The
LED stops flashing when the value returns to normal.
Log files do not recor d the exis tence of an a larm cond ition. However, when the c ontents of a log
file are viewed as a data table with the HW4 software, values that correspond to an alarm condition
are printed over a red bac kground, based on the a larm settings that HW 4 downloaded from the
logger.
Enabled, display automatically turns off after 1
minute
Display backlight
Off
Displayed parameters
%RH and temperature or temperature only
Communication protocol
RO-ASCII
Device name
Instrument model
Functions
Factory default
Humidity / temperature adjustment
Enabled
Device write protection
Disabled
Limit humidity to 100 %RH
Enabled
Out-of-limit value alarm
Disabled
Data recording
Stopped (loop mode – 10 min. interval)
Major sensor failure alarm
Enabled (cannot be disabled)
Simulator mode
Disabled
Document code Unit
Rotronic AG
Bassersdorf, Switzerland
HygroLog HL20 and HL21 data logger:
User Guide
Document title
Instruction Manual
Document Type
Page
10 of 23
2.11.4 Display-Sleep function
Using the Display Sleep f unction can substantially extend the lif etime of the battery. When the
Display Sleep function is active, the LC display of the data logger st ays blank.
The optional display of the data logger can be set to be always on. In this case, the display can be
turned on and off manuall y with the function k ey. The display ca n also be set to autom atically go
blank after 1, 5, 10 or 20 minutes.
The data logger suspends the Display Sleep func tion whenever the functio n key is pressed. The
function is also suspended when th e data logger is connected to the US B port of a PC b y means
of cable AC3006.
The main characteristics of the data logging function are as follows:
o Relative humidity values are recorded with a resolution of 0.1%RH
o Temperature values are recorded with a resolution of 0.05˚C / 0.09˚F
o Memory capacity: 20,000 single val ues or value pa irs
o Adjustable log interval: from 5 seconds to 1 hour, in increments of 5 seconds
o Two data recording modes: Loop and Start-Stop
Note:
Any recorded data pr esent in the data logger mem ory is automatically erased when ever a new
recording session is started.
Data recording modes:
Loop: when the memory is full the logger dum ps the oldest d ata sam ple and k eeps
recording. The memory retains the most recent data.
Start-Stop: the logger stops recording data as soon as the memory is full
Data recording can be stopped at any time by pressing on the function key (long key press) or with
the ROTRONIC HW4 software.
Recorded parameters:
Depending on the model, t he data logger records either tem per ature onl y or relat ive hum idit y and
temperature. A calculated valu e such as de w point can not be recor ded by the HL20 but it can be
added to the humidity and temperature data af ter do wnlo adi ng t he rec or d ed d ata to a PC with the
HW4 software. See the following HW4 manual: E-M-HW4v3-F2-018
Date and time:
The data logger has an internal real time clock that is used to associate a date and time stamp with
each data record.
When data record ing is either started or stopped using the RO TRONIC HW4 software, the real
time clock is automatically synchronized with the PC clock.
Log file format (data download to a PC with HW4):
The recorded data can b e saved as a file to a PC using ei ther HW4 or another communications
software. When using HW4, the file can be either form atted as a t ext file (extension TXT) or as an
encrypted binary file (extension LOG). The LOG file format can only be read with HW4 and complies
with the FDA / GAMP rules regarding electronic records and electronic signatures.
The LC display has a backlight which can enabled or disabled as part of the data logger
configuration. W hen the backlight is enabl ed, it turns on for a f ew seconds after press ing on the
function key.
The upper line corresponds to relative humidity or dew / frost point and the bottom line corresponds
to temperature. In the event of an alarm (out-of-limit value) the display shows the symbol [ ! ] to the
right of the value and the LED indicator flashes red.
In addition to the measur ed values, the displa y also provides inform ation such as batter y charge
and data logger status.
For configuration instructions see the following HW4 manual: E-M-HW4v3-F2-018.
o PC with the ROTRONIC HW4 software installed (version 2.4.0 or higher)
o Cable AC3006 or equivalent (connects the data logger service / data connector to a PC USB
port)
IMPORTANT:
After installing the HW 4 s oftware and prior to running HW 4, connec t cable AC30 06 to a US B port
of the PC. The PC will detec t the cable and ask for the appropriate driver. T he ROTR ONIC USB
driver (ftdibus.inf) is located in a folder named USB_Driver which is in the HW4 installation folder.
For detailed instructions see documents E-M-HW4v3-Main (§ 7.3: USB port) and
E-M-HW4v3-F2-018
Setting the Real Time Clock (required configurati on step)
The real time clock of the data logger should be set to agree with the date and tim e of the HW4
PC.
Use cable AC3006 t o connect the data logger to a USB port of the HW4 PC. Start HW 4 and
discover the data logger by selecting with the mouse the f ollowing command in the menu bar:
Devices and Groups > Search for Master Devices > USB Masters.
When the Data logger ic on app ears, left c lick with the m ouse on the (–) sign loc ated to the left of
the icon. This dis plays the functional m odules available f or the data logger. Click on the De vice
Manager module. For additional instructions, see document E-M-HW4v3-F2-018.
Other initial configuration steps
Other initial configuration steps include the following:
o Temperature measurement unit
o Log interval
o Recording mode (start-stop or loop)
For additional instructions, see document E-M-HW4v3-F2-018.
To conserve battery power, models with a display are shipped with the Display Sleep function
enabled (set to 1 minute) and with the d isplay backlight disable d. When configure d in this manner
the data logger can record data for extended periods of time
For additional instructions regarding the configuration of the display, see document
E-M-HW4v3-F2-018.
3.3 Recording and displaying data (models without display)
To start or stop recording data, pres s on the function key for a f ew s ec onds. When the
data logger is recording data, the status indicator flashes green every 5 seconds
The ROTRONIC HW4 software is required to view the measured or calculated data on a PC
monitor. Connect the data logger to the HW4 PC as explained under “Initial Start-up”. HW4 is also
required to download and save the recorded data t o disk. For additional instructions, see document
E-M-HW4v3-F2-018.
3.4 Displaying and recording data (models with display)
Displaying data
When the display sleep fu nction is enabled, the display goes blank after some time in order to
conserve battery power.
To view the measured or calc ulated data, press briefly on the functio n key. When the
display sleep function is not enabled, the display can be manually turned off by pressing
briefly on the function key.
Start or stop recording data
To start or stop rec ording data, press on this key for a few s econds. When the data
logger is recording data, thi s is indicated by the d isplay mess age bar and by the LED
indicator flashes green every 5 seconds
The ROTRONIC HW4 software is required to view the measured or calculated data on a PC
monitor. Connect the data logger to the HW4 PC as explained under “Initial Start-up”. HW4 is also
required to download and save the recorded data to disk. For additional instructions, see document
E-M-HW4v3-F2-018.
3.5 Practical advice for measuring temperature and humidity
The most comm on source of error when m easuring relative hum idity is a diff erence between the
temperature of the probe and the temperatur e of the environment. At a humidity condition of 50
%RH, a temperature d ifference of 1°C (1.8 °F) t ypically results in an er ror of 3 %RH on relative
humidity.
When using the dat a logger , it is good pr actice to allow for suff icient for tem perature eq uilibrati on
with the environment. The larger the initial temperature difference between the probe and the
environment to be measured, the more time temperature equilibration requires. This can be
monitored with the optional display.
In extreme situations, condensation may occur on the sensors when the data logger is colder than
the environment. As long as the humidity / temperature limits of the humidity sensor are not
exceeded, condensati on does not alter the calibr ation of the sensor . However, the sensor has to
dry out before it can provide a valid measurement.
Non-moving air is an ex cel l ent ins u lat or. When there is no air movement, surpr isin g d if ferences in
temperature and hum idity can noted ov er short distances. Air movement at the prob e generally
results in measurements that are both faster and more accurate.
Both the Pt 100 RTD temperature sensor and associated electronics are very stable and
should not require any calibration after the initial factory adjustment.
Long term stability of the ROTRONIC Hygromer humidity sensor is typically better than 1 %RH
per year. For m aximum accuracy, calibration of the HL20 should be verified every 6 to 12
months. Applications where the data logger is exposed to signif icant pollution may require
more frequent verifications.
Note:
Calibrating and adj usting the data logger typically requir e a humidity-tem perature generator
or other specialized equipment that may not be available to all users.
Procedure for adjusting the data logger with the ROTRONIC HW4 software:
o Use cable AC3006 to connect the service connector of the data logger to the USB port
of a PC with the ROT RONIC HW 4 software installed. Note that th e ROTRONIC U SB
driver must be installed on the PC as explained in the HW4 manual E-M-HW4v3-Main
o Start HW 4 on the PC and search f or the d ata logg er (HW 4 Main M enu Bar > Devices
and Groups > Search for USB Masters).
o Af ter finding the data logge r with HW4, expand th e device tr ee to see the data logger
functions. Select Probe Adjustment.
o For further instructions see HW4 manual E-M-HW4v3-A2-001
4.2 Firmware updates
Firmware updates will be available on the ROTRONIC website for downloading. Firmware files are
given a name that shows both to which device the file applies and the version number of the
firmware. All firmware files have the extension HEX. Procedure for updating the firmware:
o Use cable AC3006 to connect the service connector of the data logger to the USB port
of a PC with the ROT RONIC HW 4 software installed. Not e that the ROTRONIC USB
driver must be installed on the PC as explained in the HW4 manual E-M-HW4v3-Main
o Copy the firmware update file from the ROTRONIC website to the PC.
o Start HW4 software on the PC and searc h for th e data lo gger (HW4 Main M enu B ar >
Devices and Groups > Search for USB Masters).
o After finding the data logger, expand the dev ice tree t o see the data logger functions.
Select Device Manager. In the Device Manager menu bar select Tools > Firmware
Update. For instructions see document E-M-HW4v3-F2-018
The HL20 can be configured to calculate either the dew point or frost point based on the
measurement of relative humidity and temperature. The accuracy of this conversion varies,
depending on the humidity and temperature conditions as shown in the graph below:
Example: at a temperature of 20 ˚C, a dew point value of -37 ˚C is measured with an accuracy of
± 1.0 ˚C or better.
For accessories and parts such as the HW4 configuration software, service cables, calibration
accessories and spare dust filters, please see document E-M-HC2-accessories.