Istruzione / User’s Manual / Manuel d’utilisation Pag. 3 / 6
GECA S.r.l. - Via E. Fermi, 98 25064 Gussago (Brescia) Italy Tel. +39 030 3730218 - Fax +39 030 3730228
Nelle Tabelle “A” e “B” a Pag. 6, è indicata la corrispondenza tra il segnale d’uscita in mA e la % LIE.
Aprire il coperchio della custodia. Per eseguire la verifica o la taratura possono essere utilizzati due metodi.
Il primo permette di leggere direttamente il valore in mA, ed è necessario collegare in serie al morsetto "S" un multi-
metro (scala 20 mA) (Fig. 1). Tenere presente che quando si stacca il filo la centralina va in “guasto”.
Il secondo, permette, senza staccare il filo “S”, di misurare i mV corrispondenti al segnale 4÷20mA. In questo caso,
con un multimetro (Scala 200mV) posizionare i puntali sui punti TP1(+) e TP2(-) (TEST). Per trasformare il valore da mA
a mV è sufficiente moltiplicare il valore in mA x 10.
“Regolazione dello ZERO” in aria pulita il valore letto deve essere di 4mA (±0,1) oppure 40mV se misurati su TEST
(TP1 e TP2). Nel caso in cui non si riscontrasse tale valore regolare lentamente il trimmer P2 fino a ottenere il valore
richiesto.
“Regolazione del FONDO SCALA” se si dispone della bombola con la stessa
miscela Gas/aria per cui è stato tarato il trasmettitore, collegare la bombola al
portagomma del Flussometro (Fig. 2), far affluire il gas a circa 0,15÷0,3 l/min,
attendere circa 2 minuti e verificare che il valore letto sul multimetro sia:
Esempio: Se si deve verificare un sensore Mod.SE192KG tarato con Butano se
il certificato della bombola indica 0,29%v/v (=19,5%LIE) Butano e il fondo scala
del trasmettitore in %LIE è 0,3%v/v, l’uscita deve essere 19,46 (Tolleranza
±0,5mA). Nel caso in cui non si riscontrasse tale valore ruotare il trimmer P1
SPAN posto sul circuito stampato fino a leggere il valore richiesto.
GENERAL INFORMATION
The models series ST441, is a three-wire 4÷20mA linear gas detector able to detect combustible gases employing a
catalytic sensor. Two different models are available and the only difference is the calibration carried out at 20% LEL
(Lower Explosion Limit) with the specific gas:
The ST441M model should be used in plants using Methane.
The ST441G model should be used in plants using LPG.
The detector consists of a thermoplastic housing, which contains the circuit and the connection terminals; the sensor
is placed in the sensor holder on the housing cover. It is for wall installation and the protection code is IP44
The ST441 are normally connected to our gas control units for heating plants, as shown in the Table on page 6.
OPERATIONAL DESCRIPTION
The catalytic sensor is practically insensitive to humidity and temperature variations. The sensor being designed to
detect flammable gases and the calibration is carried out with the specific gas to be detected. Anyway, it can con-
temporaneously detect any other flammable gas that should be present in the same environment.
Preheating: when powered, the detector starts a time of preliminary heating of about 30 seconds. During this period
the output is 0 mA. After this period, the sensor is able to detect gas even if it attains the optimum stability conditions
after about 48 hours continual functioning.
Therefore, after that time we advise to check in clean air the “4 mA” output. If is necessary “4mA calibration” can be
carried out as explained later in FUNTIONAL TESTING. This calibration is necessary to adjust the sensor to the
environment conditions.
Faults: In case of sensor damage, the "S" output falls down to 0 mA (FAULT). The signal is then indicated as a
damage situation. This happens also when an interruption to the connection wires between the detector and the
control unit occur.
Periodical testing: we advise to carry out working tests every 6-12 months. After 2 year, we advise to proceed to
the recalibration of the circuit with Gas/Air mixture as explained later in FUNTIONAL TESTING.
INSTALLATION
The detector should be installed according to the national disposition in force on the matter.
Model ST441M positioning: Methane (CH
4
) is a gas lighter than air. Its density related to air is 0.55; its LEL (Lower
Explosion Limit) is 4.4% volume. The instrument should be fixed at 30 cm from the ceiling and be placed at 1-1.5 meter
from the gas appliance, far from the room corners or from ventilation intakes.
Model ST441G positioning: LPG is a gas mixture composed by 20-30% Propane (C
3
H
8
) and by 70-80% Butane
(C
4
H
10
). LPG calibration must be carried out with Butane which is a gas heavier than air. Its density related to air is
2 and its LEL (Lower Explosion Limit) is 1.4% volume. The instrument should be fixed at 30 cm. from the floor and be
placed at 1-1.5 meter from the gas appliance, far from the room corners or from ventilation intakes
Mounting: The Fig. 2 shows the instrument size. It has to be wall-mounted by two screw anchors.
Cable glands: the lower side of the housing has 3 inputs designed for metric cable glands (M16x1.5 that accept
external cables Ø 4÷9 mm). These passages are closed, but they are not manually breakable, according to the
installation requirements, they must be drilling. To facilitate the operation, they have a centering for the drill bit.
Electric connections: are to be carried out using the three-pole non-reversible and plug-in terminals. (See special
instructions enclosed with the gas detectors). It is not necessary to use shielded cables.
The transmitters can be placed at a max. distance of 100 meters from the gas detector when 3x1.5mm
2
cables are
used, and 200 meters with 3x2.5 mm
2
cables.
19,46 = 4
0,3
0,29 x16
mA
(195) 194,6 10 x19,46 mV
4
%v/v in Sensore Scala Fondo
Bombola Gas%v/v x16
mA
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