Mounting And Connections - WIKA mw series Instruction Manual

6.5.1
Calibration of dead band
The calibration of the dead band is obtained using the following
procedure:
1 - Raise pressure in the circuit until reaching the set point and
record its value (Pi).
2 - Reduce pressure in the circuit until reaching the reset point
and record its value (Pr).
3 - The difference Pi - Pr = Va represents the dead band factory
adjusted value.
4 - Rotate the adjustment wheel in the sense shown in Fig. 6 plac-
ing letter B on the mark.
5 - Repeat operations 1 and 2 and measure the new dead band
Vb.
6 - By comparing the values Va and Vb approximately determine
the letter of the wheel to be placed on the mark.
7 - Place the mark and measure the obtained dead band.
8 - Proceed by successive approximations until reaching the de-
sired dead band value with enough accuracy.
9 - Then proceed with the set point calibration
Example: The dead band increase corresponding to the rotation
from A to B is given by: Vb - Va =I
The desired dead band V will be approximately in the position in-
dicated by the value K 
V I
- By units, the letters of the wheel (1=A, 2=B, 3=C, 4=D, 5=E,
6=F)
- By decimal digits, the percentage middle position between
the located letter (of units) and the following one.
6.6
FINAL OPERATIONS
Disconnect the instrument from the calibration circuit.
6.6.1
Weatherproof pressure switches (Model MW)
Take the cover, ensure that the sealing gasket is correctly fitted
into its seat, and insert the cover onto the case, with the blocking
gap positioned in correspondence to the blocking bracket.
Turn the cover clockwise closing it tightly. Mount the blocking de-
vice as in Fig. 4. Mount on pressure connection and cable entry
the protection caps supplied with the instrument.
6.6.2
Flameproof pressure switches (Model MA).
Screw on the cover and block it using the headless screw with
which it is equipped (Fig. 5)
Mount on pressure connection and cable entry the protection caps
supplied with the instrument.
Caution: The protection caps should only be definitively removed
during the connection steps (see § 7).
7

MOUNTING AND CONNECTIONS

7.1
MOUNTING
Surface mount the instrument by means of the holes provided, or
pipe mount using the appropriate bracket or mount directly on pro-
cess in a vertical position (with the pressure connection down-
wards) (See fig. 17,18,19,20,21 and 22).
In case of surface or panel or rack mounting the instruments can
be mounted side by side (see Fig.19). The chosen position must
be such that vibrations, the possibility of shocks or temperature
changes are within tolerable limits.
With gas or vapour process fluid, the instrument must be posi-
tioned higher than the pipe inlet (see Fig. 22). With a liquid process
fluid, the instrument can be positioned higher or lower, indifferently
(see Fig. 21 and 22). ). In this case, during set point calibration the
negative or positive head must be taken into account.
CAUTION: (Instruments MA, MAH, MAG, MW, MWH and MWG)
positions other than vertical are allowed provided environmental
conditions do not cause condensation to form or water to enter the
instrument through the ventilation path (Version MA (*) fig.5). The
instruments versions MWB and MAB must be installed in vertical
position (process connection towards).
7.2
INSTRUMENT WITH DIAPHRAGM SEALS
When the pressure switch is mounted on diaphragm seal with ca-
pillary and the set point is less than 10 bar, the gap (distance h)
between diaphragm seal and instrument generates a column of
liquid, whose pressure equivalent constitutes a drift of set point.
The set point has to be adjusted consequently.
INSTRUCTION MANUAL
which expresses:
Fig. 7 – Instrument with diaphragm seal
7.3
PRESSURE CONNECTIONS
For a correct installation it is necessary to:
Mount a shut-off valve with drain (root valve) on the process tube
to allow the instrument to be excluded and the connection tubing
to be drained. It is recommended that said valve has a capstan-
blocking device aimed at preventing it being activated casually and
without authorisation.
Mount a service valve near the instrument to permit possible func-
tional verification on site. It is recommended that the service valve
is closed with a plug to prevent the outlet of the process fluid
caused by the incorrect use of said valve.
Mount a three-piece joint into the process connection to permit the
easy mounting or removal of the instrument itself.
The pressure connection adaptor have to be installed as per Fig.8
Fig. 8 – Installation of pressure connection adaptor
Carry out the connection to the process using a flexible tube in
such a way that variations in the temperature of the tube itself do
not force the instrument attachment.
Ensure that all the pressure connections are airtight. It is important
that there are no leakages in the circuit.
Close the root valve and the relative drain device. Close the ser-
vice valve using a safety plug.
7.4
INSTRUMENTS WITH PROCESS CONNECTION COATED
WITH PTFE
The pressure connection must be made in such a way that the part
protruding from the instrument have to be used as a sealing ring.
Fig.9 - Instrument with process connection coated with PTFE
7.5
ELECTRICAL CONNECTIONS
It is recommended to carry out the electrical connections according
to the applicable standards.
In case of flameproof instruments and intrinsic safety instruments
see also the Standard IEC/EN-60079-14. If the electrical connec-
tion is carried out in a protected tube, it shall be made so that con-
densate is prevented from entering instrument enclosure.
To guarantee the ingress protection IP66 and prevent loosening of
the blocking joint or cable glands, it is prescribed to seal the
threads with an anaerobic sealant. For example, use a sealant like
Loctite ® 542.
NI-221WE
Rev. 5 12/16
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