Lufft 8810.U051 User manual

www.lufft.com
Operating Manual
ARS31Pro-UMB
ARS31-UMB
Active Road Sensor
Order No. ARS31Pro-UMB: 8810.U051 50m cable
Order No. ARS31-UMB: 8610.U050 50m cable
Version V6 (06/2014)

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 2
Contents
1Please read before commissioning ........................................................................................................3
1.1 Symbols used.....................................................................................................................................3
1.2 Safety instructions ..............................................................................................................................3
1.3 Designated use...................................................................................................................................3
1.4 Guarantee...........................................................................................................................................3
1.5 Incorrect use.......................................................................................................................................3
1.6 Nomenclature .....................................................................................................................................3
2Differences between ARS31Pro-UMB/ARS31-UMB..............................................................................4
3Device description ..................................................................................................................................4
3.1 Method of operation ARS31Pro-UMB/ARS31-UMB...........................................................................4
3.2 Additional features of ARS31Pro-UMB...............................................................................................5
3.3 Availability of measurement values....................................................................................................5
4Installation...............................................................................................................................................7
4.1 Preparation.........................................................................................................................................7
4.2 Installation...........................................................................................................................................7
4.3 Connecting the cable........................................................................................................................11
4.4 Commissioning and testing ..............................................................................................................14
5Maintenance.........................................................................................................................................15
5.1 Replacing the sensor system ...........................................................................................................15
5.2 Connections......................................................................................................................................16
6Configuration ........................................................................................................................................18
6.1 Factory settings ................................................................................................................................18
6.2 Using PC configuration software......................................................................................................18
6.3 Firmware update...............................................................................................................................22
7Communication.....................................................................................................................................23
7.1 Binary protocol..................................................................................................................................23
7.2 ASCII protocol...................................................................................................................................25
7.3 Channel assignment for the data request ........................................................................................26
7.4 Mapping standards...........................................................................................................................28
8Technical data ......................................................................................................................................29
8.1 Measurements..................................................................................................................................29
8.2 Storage conditions (complete sensor)..............................................................................................29
8.3 Operating conditions.........................................................................................................................30
8.4 Electrical data...................................................................................................................................30
8.5 Interfaces..........................................................................................................................................30
8.6 Mechanical data (excluding cable)...................................................................................................30
9EC Certificate of Conformity.................................................................................................................31
10 Troubleshooting....................................................................................................................................32
11 Service and maintenance.....................................................................................................................33
12 Disposal................................................................................................................................................33
13 Manufacturer.........................................................................................................................................34
13.1 Technical support .............................................................................................................................34
Version history:
Version
Date
Edited by
Comments
1
21.08.2012
LA/BR/FS
First version
2
17.09.2012
LA/BR/FS
Technical data modified, adjustment to current public standards
3
10.04.2013
FS
Supplements to the cable length and to the installation
4
18.04.2013
FS
Extension cable table was added
5
12.03.2014
LA/BR/RR
Modification of Certificate of Conformity, clarification of the technical data (freezing temperature)
6
04.06.2014
LA/BR
Supplements to the cable length and power supply, integration of ARS31-UMB

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 3
1 Please read before commissioning
Before using the equipment, please read the operating manual carefully and follow the
instructions in every detail.
This operating manual covers ARS31Pro-UMB/ARS31-UMB device version 9 and above
and firmware 10.3 and above.
1.1 Symbols used
Important indication concerning possible hazards to the user
Important indication for the correct functioning of the equipment
1.2 Safety instructions
Installation and commissioning must only be carried out by suitably qualified specialist
personnel.
Never take measurements on or touch live electrical parts.
Pay attention to the technical data and storage and operating conditions.
1.3 Designated use
The equipment must only be operated within the range of the specified technical data.
The equipment must only be used under the conditions and for the purposes for which
it was designed.
The safety and operation of the equipment can no longer be guaranteed if it is modified
or adapted.
Do not continue to use equipment that is obviously defective.
1.4 Guarantee
The guarantee period is 12 months from the date of delivery. The guarantee is forfeited if
the designated use is violated.
1.5 Incorrect use
If the equipment is installed incorrectly
-It may not function
-It may be permanently damaged
If the equipment is not connected correctly
-It may not function
-It may be permanently damaged
-There may be a possibility of an electrical shock
1.6 Nomenclature
Tg: Freezing temperature that the sensor identified
Tu: Road surface temperature, ambient temperature
Toi: Threat of icing

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 4
2 Differences between ARS31Pro-UMB/ARS31-UMB
ARS31Pro-UMB compared with ARS31-UMB possesses the following features:
Measurement of threat of icing by means of a direct measurement or freezing
temperature.
Exact measurement of road surface temperature with an external temperature
sensor.
3 Device description
Active Road Sensor ARS31Pro-UMB/ARS31-UMB serves to determine the freezing
temperature of a liquid on the road surface. It can be used to measure the following data:
Salt concentration (NaCl, CaCl and MgCl)
Product concentration (potassium acetate, potassium)
Freezing temperature (independent of mixture)
The sensor excels further due to the following features:
Compact design and easy installation
Low maintenance
Parts can be replaced without uninstalling the device
Data transfer via RS485
Internal electrical isolation of power supply
ESD protection on all interfaces
Inverse-polarity protection
3.1 Method of operation ARS31Pro-UMB/ARS31-UMB
ARS31Pro-UMB/ARS31-UMB determines the freezing temperature of a liquid on the road
surface by means of active cooling and heating. The Sensor allows precise determination
of the freezing temperature in the absence of accurate knowledge of the type or mixture of
salt.
The sensor operates in a temperature range described in the chapter 8.3 Operating
conditions.
The freezing temperature is calculated for road surface temperatures of less than 5°C
(adjustable between 2°C and 10°C). The lowest possible freezing temperature that can be
calculated is about 20°C below the current road surface temperature, for details see
chapter 8.1.1 Freezing temperature.
The sampling rate for freezing point measurement in the sensor is configurable and may
be set to 20, 30 or 60 minutes (factory settings: 20 minutes). If the ambient conditions so
require, the sensor extends its measurement cycle by up to 10 minutes if necessary.
To avoid measurement gaps due to interference during measurement, the sensor is
equipped with an intelligent “hold measurement” function for freezing temperature.

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 5
If there is no freezing temperature / salt concentration detected in a measuring cycle the
last identified freezing temperature will be delivered for the following 40 minutes (default:
40 –interval can be adjusted). During this interval the freezing temperature can only move
to 0°C if the sensor definitely detects clear water on the road.
The freezing temperature profile is smoothed by the sensor. This function can be disabled
using the UMB-Config Tool.
Data polling takes place through any desired host computer which supports any of the
communication protocols described in Section 6 and disposes of an RS485 interface.
Measurements are polled and transmitted over an RS485 interface.
The device is connected using a 4-core cable.
Windows PC software is available for configuration and measurement polling during
commissioning.
3.2 Additional features of ARS31Pro-UMB
In addition, ARS31Pro-UMB determines the threat of icing as follows: for a dry road –by
cooling to an adjustable temperature value (∆ T1); for a wet road - by comparing the
measured freezing temperature with the road surface temperature while taking account of
the set temperature value (∆ T2).If a threat of icing is determined using one of the methods
described above, the sensor transmits “threat of icing”.“Threat of icing” is only transmitted
as a result of a direct measurement if the road temperature ∆T is less than +1°C.
To avoid measurement gaps due to interference during measurement, the sensor is
equipped with an intelligent “hold measurement” function also for threat of icing.
If the condition “threat of icing” was triggered by the freezing temperature measurement
and the freezing temperature enters the hold state, the condition “threat of icing” is also
updated via the last determined freezing temperature and the current road temperature. In
this case, updating of the threat of icing ends simultaneously with the updating of freezing
temperature. However, if during updating the threat of icing is actively determined by
means of a direct measurement, this condition is retained for the set period.
With external sensor the road surface temperature is determined exactly.
3.3 Availability of measurement values
After a successful measurement, the measurement values are available for query until new
measurement values are available. Synchronization between query and measurement
cycle is not needed. It is recommended to poll the sensor every minute. Within the
measurement interval the measured values are immediately updated when they become
available. Due to different environmental conditions the timing of the availability of
measurements can alter in the measurement interval, the measurement values are
therefore not necessarily updated in the grid of the selected measurement interval.

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 6
Example: Measurement interval 20 minutes
Start measurement
Start measurement
Start measurement
Start
TG 1
availa
ble
TG 2 available
TG 3
availa
ble
0
min
5
min
10
min
15
min
20
min
25
min
30
min
35
min
40
min
45
min
50
min
55
min
60
min
1) At time 15 min TG 1 is available and will be issued
2) In the next measurement cycle, at the time 25 min GT 2 is determined and issued. So
TG1 was issued for 10 minutes.
3) In the next measurement cycle, at the time 25 min GT 3 determined and issued. So TG2
was issued for 30 minutes.

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 7
4 Installation
The road sensor is installed in the middle of the carriageway. If the road has two lanes, the
sensor is installed in the left hand lane.
4.1 Preparation
The sensor ARS31Pro-UMB/ARS31-UMB requires a hole of diameter Dm > 16 cm and
depth Dp = 6 cm. A slit of width W = 2 cm and depth Dp = 5 cm is cut into the road for the
cable.
For ARS31Pro-UMB the external sensor requires an additional hole of diameter Dm > 9
cm and depth Dp = 5 cm.
Attention! When installing on bridges, make sure that the insulation layer is not
damaged (it is not always possible to maintain a depth of 6 cm in these cases).
4.2 Installation
Warning: Do not undo the cable connections under any circumstances
You can only cut the cable at the control panel end.
The cable must be laid in a protective tube in such a way as to ensure that any expansion
of the road covering does not affect the cable. The road sensor cables must not be
subjected to tensile force during installation.
Warning: Damage to the cable sheath or external sensors causes water ingress into
the sensor. Sensors with damaged cables must not be installed and can only be
repaired by Lufft.
Install the road sensor in the hole provided in such a way that it is flush with the road
surface. To do this, place the installation aid - which is already mounted on delivery - on
the road surface. It may be necessary to align the sensor by bending the installation aid.
Under no circumstances must the road sensor project beyond the surface of the
road covering (damage due to snow-clearers).
Fill the cavities with casting resin concrete.
Only use concrete bedding systems whose temperature remains below 80°C on
hardening as otherwise the road sensor will be damaged.
After the casting resin concrete has hardened, remove the installation aid and the green
protective film. Reinstall the fixing screws of the installation aid in the open holes of the
sensor (torque 2 Nm).




Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 8
4.2.1 Enlarging the cable (for example 100m):
Important: the original cable must be shortened and extended from the shortest possible
distance (5m roadside). The loop resistance of the overall cable must not exceed 5 Ω!
For example, extension of 100 m with a 0.5 mm² cable of 73.2 Ω/km loop resistance and
parallel connection of 4 cores each:
Per core 100 m cable results in a loop resistance of 7.3 Ω.
By parallel connection of 4 cores results in a loop resistance of 7.3 Ω/ 4 = 1.83 Ω
Sample extension-box

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 9
Extension Cable Table for ARS31Pro-UMB/ARS31-UMB
Active Freezepoint Sensor
Explanations:
Recommended extension cable: A-2YF(L)2Y Nx2x0,8 or similar
Wirebundle 2x (2 times) means 2 pair of wires e.g. 2x2x0,8 because
2 single wires are 1 pair for power supply (+&-)!
RS485 Terminator resistor required means that either at Sensor
input port or at muffle position a resistor of 120 Ohm should be
connected parallel to the RS485 2-wire interface.

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 10
The power consumption changes with change in the cable length:
The sensor will have a capacity of max. P = 30W needed.
R1 + R2 = loop resistance
U = Voltage in the cabinet at the end of the cable (24V)
US = voltage at the sensor
I = supply current
I is calculated with the equation  
󰇛󰇜  󰇛󰇜
or  
󰇛󰇜󰇡
󰇛󰇜󰇢 
󰇛󰇜

For the calculated case with loop resistance 1,83 Ω:

󰇛󰇜 󰇛󰇜  󰇛󰇜

Not considered here is the short piece of the standard cable!

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 11
4.3 Connecting the cable
The road sensor cable is connected in the control panel together with the power supply
and the bus system, e.g. ISOCON-UMB.
The screening of the connection cable MUST be laid to ground.
Example of a standard Lufft UMB cabinet as well as examples of the grounding of the shield
There are two existing cables: color coded and numerical coded.
Connection to the road sensor cable:
1 White Negative power supply
2 Brown Positive power supply
3 Green RS485_A
4 Yellow RS485_B
Illustration 1: ISOCON-UMB connection
Warning! Connecting the cables incorrectly will destroy the road sensor!

Sensor voltage output 24 V
ARS31 sensor interface


Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 12
Illustration 2: Installation of ARS31PRO-UMB/ARS31-UMB in the road
Straßensensor
Road sensor
Straßensensor
Road sensor
ext.
Temp.Sens.
ext.
Temp.Sens.
min. Ø 16 cm
Schlitz/slit:
2 cm breit / wide
5 cm tief / deep
Straßenoberfläche
Road surface Gießharzbeton
casting resin concrete
Gießharzbeton
Casting resin conrete
Straßenoberfläche
Road surface
5 cm
6 cm
min. Ø 9 cm
59 cm
67,5°
ARS31Pro extension

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 13
Illustration 3: Installing the ARS31PRO-UMB/ARS31-UMB
externer
Temp.Sens.
externer
Temp.Sens.
Gießharzbeton
Casting resin concrete
6 cm
Montagehilfe
Installation aid
Innensechskant
Hexagon socket head screw
Straßensensor
Road sensor
Innensechskant
Hexagon socket head screw
Straßensensor
Road sensor
Gießharzbeton
Casting resin concrete
Straßenoberfläche
Road surface
Montagehilfe
Installation aid
ARS31Pro extension

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 14
4.4 Commissioning and testing
After the device has been installed and connected correctly, the ARS31Pro-UMB/ARS31-
UMB is initialized and measurement begins. The first measurements are available after
approximately 1 minute; after approximately 20 minutes, the measurements for freezing
temperature and saline concentration / threat of icing are available (provided that the
ambient conditions allow such measurements).
The functionality of the road sensor must be checked after it has been installed. The
sensor must be connected to an evaluation unit (e.g. PC with UMB-Config Tool) for this
purpose. Communication between sensor and evaluation unit must be checked for perfect
operation.

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 15
5 Maintenance
Maintenance should be carried out on the road sensor once annually. This includes the
visual inspection of the housing. It is recommended to clean the surface of the sensor if it
is heavily soiled. Sensor replacement is recommended in the event of significant
mechanical damage to the sensor. This also applies if the sensor’s plastic insert is
severely worn.
5.1 Replacing the sensor system
If the road sensor’s plastic insert becomes unusable due to mechanical effects, or the
sensor is damaged, the plastic insert can be replaced with no need to replace the entire
housing.
Attention: Only replace the sensor system when the road is dry
To uninstall the plastic insert, remove all six hexagon socket head screws. There is a small
opening on the edge of the cover suitable for inserting a screwdriver. This allows you to lift
out the plastic insert. Make sure that the connection cable on the underside of the sensor
has not broken off. The connectors must be pulled out without putting a strain on the cable.
The housing must be cleaned thoroughly before installing the new sensor. Even small
impurities on the seat of the seal can cause the sensor to fail in the long term. No moisture
must be trapped in the housing!
On connecting the connector to the new sensor, make sure that you do not touch the
sensor electronics. Electrostatic discharge (ESD) destroys the sensor.
The seal must be greased with silicone grease prior to insertion. The seal must not bend
out of line on installing the plastic cover. You should also make sure that the thermal
conducting foil on the under edge of the housing is not displaced during installation. The
plastic cover must be inserted into the housing without the use of force. There is only one
possible installation position: The apertures on the copper head of the sensor must
point in the direction of the cable glands on the housing. The threads of the fixing screws
must be greased. First the screws are attached loosely and then tightened cross-wise
(torque 2 Nm).




Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 16
5.2 Connections
5.2.1 Cable
See Section 3.3 Installation –Connecting the cable
5.2.1.1 Power supply
The ARS31Pro-UMB/ARS31-UMB power supply is 24 VDC ± 10% (for a cable length up to
15 meters).
For cable lengths over 15 meters see table below. The supply voltage must not exceed the
value of 28 VDC.
cable lengths
[m]
recommended power supply
[VDC]
≤15
24
20
24,6
25
25,1
30
25,7
35
26,3
40
26,8
45
27,4
50
28
The power supply unit used must be approved for operating devices of protection class III
(SELV).
5.2.1.2 RS485 interface
The device has a half-duplex, 2-wire RS485 interface with the following settings:
Data bits: 8
Stop bit: 1
Parity: none
Adjustable baud rates: 1200, 2400, 9600, 19200, 38400 (standard: 19200 bit/s)
Please do not change the baud rate of the sensor unless it is absolutely essential. If
the sensor is operated via ISOCON-UMB, the baud rate of the sensor must match the
set baud rate on the ISOCON-UMB.
The screened cable MUST be laid to ground in the control cabinet
If the device is not connected properly:
-It may not function correctly
-It may be permanently damaged
-There is a danger of electric shock under certain circumstances
5.2.2 Connections in the housing
There is a single 4-pole terminal block on the underside of the plastic insert. This serves to
connect the power supply and the interface to the associated cable.



Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 17
Power supply connection assignment/RS485:
Pin
Assignment
1
GND
white
2
V+, 24 V
brown
3
A (Rx+)
green
4
B (Rx-)
yellow
The data and power supply cables are connected via a 4-pole terminal block. Cable type
LI-2YCYv2X2X0.5 is used.
Cable labeling on the pins is based on DIN 47100.
The screened cable must be laid to the ground circuit connector in the control panel.

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 18
6 Configuration
Lufft provides PC software for configuration purposes UMB-Config Tool. Using this
software, the user can adjust the sensor according to his needs.
Starting from Firmware V10.3 the UMB-Config Tool version 2.2 or
newer must be used.
6.1 Factory settings
The factory settings of the ARS31PRO-UMB are as follows:
Device ID: 1
Class ID 4
Baud rate: 19200
RS485 protocol: binary
6.2 Using PC configuration software
The main functions of the configuration software are described in detail in the Online Help.
For this reason only the sensor-specific menus and functions are described here.
6.2.1 Configuration of ARS31Pro-UMB
After loading an ARS31PRO-UMB configuration, all relevant settings and values can be
adjusted.
If several ARS31PRO-UMB devices are operated on a UMB network, the ID must be
changed before connection to the network, as each device requires a unique ID. IDs are
allocated in ascending order, beginning with number one.
The measuring rate indicates how often a new measuring cycle is started. This value is
configurable and can be set to 20, 30 or 60 minutes (factory settings: 20 min.)
If there is no freezing temperature / salt concentration detected in a measuring cycle the
last identified freezing temperature will be delivered for the following 40 minutes (default:
40 –interval can be adjusted). During this interval the freezing temperature can only move
to 0 if the sensor definitely detects clear water on the road. The interval for maintaining the
freezing temperature can be configured in the UMB-Config-Tool and can adopt values
between 20 and 120 minutes (default 40 minutes). The function can be deactivated by
unticking the option “FT data hold active”.
With the option "FT smoothing operator active", a smoothing function for the freezing
temperature can be activated. The operator itself can be set between 0 (maximum
smoothing, no change in the FT) and 100 (no smoothing). After activating this function a
start value of 40 is set for the smoothing operator. This value can be adjusted if necessary.
Freezing temperature / threat of icing is detected when road temperatures are lower than
the road temperature threshold. If the road temperature is higher than this threshold,
freezing temperature / threat of icing is not detected. The threshold value is adjustable
between 2°C and 10°C.
The dry threshold defines the measured value on the ARS31PRO-UMB from which a dry
road is assumed and the freezing temperature is no longer measured; instead of the
freezing point measurement, detection of threat of icing then takes place. In the factory


Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 19
setting, the sensor adjusts its dry threshold daily. If this function is disabled, the dry
threshold as set using the UMB-Config Tool applies.
If this value is too high, the ARS31Pro-UMB measures during dry conditions, which may
lead to incorrect measurements caused by condensation on the sensor element.
The following parameters serve to configure detection of the threat of icing:
Time x describes the time for which the sensor cools down in order to cause the formation
of dew or frost.
Delta T (∆ T) is the temperature difference by which the road surface temperature cools
down in order to measure the threat of icing via the formation of dew or frost.
Delta T2 (∆ T2): If the threat of icing is detected via the temperature difference between
the road temperature and the freezing temperature, ∆ T2 describes the temperature
difference for which, upon lower deviation, threat of icing is transmitted. A value of -50°C
deactivates the calculation of threat of icing using the freezing temperature (available with
firmware release 10.3).
Delta LFM% describes the required change in the critical measurement variable for the
detection of the threat of icing. Higher numerical values reduce the probability of the
sensor transmitting the threat of icing and increase the stability of this function.

Operating Manual ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany 20
6.2.2 Configuration of ARS31-UMB
After loading an ARS31-UMB configuration, all relevant settings and values can be
adjusted.
If several ARS31-UMB devices are operated on a UMB network, the ID must be changed
before connection to the network, as each device requires a unique ID. IDs are allocated in
ascending order, beginning with number one.
The measuring rate indicates how often a new measuring cycle is started. This value is
configurable and can be set to 20, 30 or 60 minutes (factory settings: 20 min.)
If there is no freezing temperature / salt concentration detected in a measuring cycle the
last identified freezing temperature will be delivered for the following 40 minutes (default:
40 –interval can be adjusted). During this interval the freezing temperature can only move
to 0 if the sensor definitely detects clear water on the road. The interval for maintaining the
freezing temperature can be configured in the UMB-Config-Tool and can adopt values
between 20 and 120 minutes (default 40 minutes). The function can be deactivated by
unticking the option “FT data hold active”.
With the option "FT smoothing operator active", a smoothing function for the freezing
temperature can be activated. The operator itself can be set between 0 (maximum
smoothing, no change in the FT) and 100 (no smoothing). After activating this function a
start value of 40 is set for the smoothing operator. This value can be adjusted if necessary.
Freezing temperature is detected when road temperatures are lower than the road
temperature threshold. If the road temperature is higher than this threshold, freezing
temperature is not detected. The threshold value is adjustable between 2°C and 10°C.
The dry threshold defines the measured value on the ARS31-UMB from which a dry road
is assumed and the freezing temperature is no longer measured.
If this value is too high, the ARS31-UMB measures during dry conditions, which may lead
to incorrect measurements caused by condensation on the sensor element.
In the UMB-Config-Tool the temperature limit of the freezing temperature can be adjusted
if necessary (factory setting: 0, this means no limit for freezing temperature).
After the activation of the freezing temperature limit, the smoothed freezing temperature
can be transitional-wise under the temperature limit (if the freezing temperature directly
before the change was under the opposed limit).