Datasheet

DATA SHEET
Technical changes reserved
0141 0316-159 07/2014
Functional description
The dew formation module is a universal, resistive evaluation circuit
for dew formation sensors SHS A3, A4L, A5. The module has a three
pole socket strip for connection of the sensor and a 4-pole clamp
terminal for operating voltage and relay output. The scope of supply is
without sensor element, please separately order the required sensor
element!
In principle, the module together with the sensor is an electronic
hygrostat for high humidity range, which is meant for recognising dew
formation or beginning of condensate formation on objects. As soon
as the measured value of surface humidity exceeds a certain dened
limit (approx. 94% RH), the relay contact opens and the static current
loop is interrupted (safety function). The signal can be used, for
example, for switching ON a dryer or a heater.
In application of SHS A5 as sensor element if a conductance sensor,
(integrated on the sensor in addition to the resistive sensor element)
is also evaluated, then it recognises already occurred dew formation.
With the latest measuring principle and application of SHS-dew
formation sensors with logarithmic characteristics, it is possible to
capture the dew formation threshold before condensate formation.
The module is protected against over voltage, reverse polarity and
wrong connection by means of varistor and protection diodes. The
connections are done through a 4-pole terminal.
Application notes
Because of the optimised AC-circuit technology, the sensor survives
short-term wetting with condensate, without the sensor getting dam-
aged due to electrolysis effects. Nevertheless, continuous contact
with water should be avoided.
A representative climate condition must prevail at the measuring loca-
tion. Air breeze or heat sources can disturb the functioning.
In the application of module as dew formation monitor, the sensor ele-
ment must be installed at the coldest location. Perfect functioning is
only guaranteed, if there is no air gap between the mounting surface
and sensor element. If necessary, mount by using thermal conducting
paste or stick together with ceramic lled epoxy resin adhesive.
Care should be taken that the electronics of the module is protected
against any possible condensate formation. If electronics is installed
too close to the cold object, then condensate can develop on the
module, resulting into failure. An extension of the connections to the
sensor is possible, but because of EMV considerations, the con-
nection length should be kept as short as possible. Shielded cables
should be used.
Connection layout
The power voltage supply is with 24 V~ or 24 V DC, operating current
max. 7 mA. The contact output is a galvanically isolated, wear-free
semi-conductor relay, which can switch DC or AC, switching voltage
max. 36 V, switching current max. 25 mA.
Pin Name Function
1 SW1 Switching contact, potential free, closed in dry
condition
2 SW2 Switching contact, potential free, closed in dry
condition
3 AC1/DC- Operating voltage 24 V AC or negative operating
voltage
4 AC2/DC+ Operating voltage 24 V AC or positive operating
voltage
Connection diagram
Operation with AC
Operation with DC
The power supply and output are potentially isolated and protected
against over voltage and transients with the help of a varistor. On
operation with DC voltage and triggering inductive loads, a diode
should be additionally put in the circuit.
Sensor element connection
The resistive sensor surface of the dew formation sensor is connec-
ted between pin 1 and 3 of the sensor plug. The connections of SHS
A3 and SHS A5 t directly into the contact strip.
If SHS A5 is being used, then the common connection of the resistive
element and comb structure is at pin 1 (COM).
Pin Name Function
1 COM Resistive sensor element or common connec-
tion for SHS A5
2 SEN1 Optional conductance switch for dew formation
sensor SHS A5
3 SEN2 Resistive sensor element
DEW FORMATION MODULE
SHS-MOD-LC
B+B Thermo-Technik GmbH | Heinrich-Hertz-Straße 4 | D-78166 Donaueschingen
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