Datasheet

DATA SHEET
Technical changes reserved
0141 0316-128 07.2013
Distribution Box for Temperature
Measuring System, 10 Sockets RJ12
Hub
For connection of multiple probes, a hub is available with 10 ports
(RJ12). One port is used for connection of temperature logger, and
if necessary, another port is used for connection of another hub. As a
result, 8 to 9 ports are available for connection of temperature probes.
The hub has a supply capacitor and a pullup resistance of 10 kΩ for
compensation of connection capacitance. An RJ12 cable (1 m) is also
included in the scope of supply of hub, which is required for connection
to a PC adaptor or for cascading with another hub.
Connection cable
For short connection lengths, there are no special requirements for the
cable to be used. With unshielded cable, a larger connection length
can be obtained in an undistorted environment, since the capacitive
bus load is less. With additional measures, a total length of 60 m or
more can be achieved without any problems.
In disturbed environment, the cable should be shielded in order to
improve the noise immunity of the system. Due to higher capacitive
loading, the maximum possible connection length is less for a shielded
cable.
Increase in connection length
The sum total length of all connection cables should be within around
60 m to ensure reliable functioning. By wiring of an additional pullup
resistance of 1.5 to 10 kΩ (Line DATA against +5 V), the cable length
can be increased with minor deterioration in measuring accuracy due
to higher self heating of the sensors.
Temperature range
The Dallas temperature sensors are semiconductor sensors. The un-
housed sensors are suitable for temperature measurement in the ran-
ge of –55 … +125 °C. These temperature values are the nal limits and
operating above these values is not at all recommended, otherwise the
component can get damaged.
In addition, the allowable application temperature also depends on the
connection cable and type of protection sleeve used. PVC insulated
cable gets hard and brittle below -10 °C and hence should not used at
these lower temperatures otherwise the insulation may crack.
Above 60 °C continuous operating temperature, the PVC becomes soft
and can get deformed. At approx. 80 °C, the material becomes plastic
and the insulation gets damaged under pressure.
Installing and conguration
The Dallas temperature sensor of type 1820 has an internal identi-
cation (serial number) and can be operated in parallel together with
several other components on a three-wire bus. After wiring all the sen-
sors, the PC adapter must be individually congured for the connected
sensors. Operation is not possible without prior conguration of the
system. Since the conguration is stored in the internal EEPROM of
adapter, this process is to be done only once. Only if an additional
sensor is to be used on the existing network, the conguration needs
to be repeated.
The sorting of probes, found on the network, is done on the basis of
binary serial number.
Pin conguration of RJ12-plug connector
The Western-plug connector is congured as follows (View on the
cable, i.e. contact surfaces of the plug!):
1 Shielding or unoccupied
2 Ground
3 Dallas Data or unoccupied
4 Dallas Data
5 +5 V
6 +5 V or unoccupied
In 4-core at cable, PIN 1 and PIN 6 are not occupied. PIN 3 and 4 are
bridged together at the PC-adapter. Only PIN4 is needed to connect
the data line of the sensor.
Measuring accuracy
The sensors are calibrated during manufacture and have a typical
measuring accuracy of ±0.5 °K at 23 °C application temperature. At
the upper and lower limit of measuring range, the accuracy is some-
what on the lower side. Further information is available in the data
sheet of component at the website of manufacturer.
During all temperature measurements, the physical conditions are also
to be taken care of in order to avoid measuring error, which mainly
decides the precision of measuring arrangement.
B+B Thermo-Technik GmbH | Heinrich-Hertz-Straße 4 | D-78166 Donaueschingen
Fon [phone] | Fax [phone] | [e-mail] | bb-sensors.com
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