General Notes; Operating Principle; Model Code; Identification Plate And Markings - WIKA mw series Instruction Manual

1

GENERAL NOTES

1.1
FOREWORD
The wrong choice of a model/ version, as well as the incorrect in-
stallation, lead to malfunction and reduce instrument life. Failure to
abide by the indications given in this manual can cause damage to
the instrument, the environment and persons.
1.2
ALLOWED OVERRANGE
Pressure exceeding the working range can be occasionally toler-
ated provided they remain within the limits stated in the instrument
features (vacuum or proof pressure). Continuous pressures ex-
ceeding the working range can be applied to the instrument pro-
vided they are clearly stated in the instrument features. The current
and voltage values stated in the technical specifications and rat-
ings must not be exceeded. Transitory overages can have a de-
structive effect on the switch.
1.3
MECHANICAL VIBRATION
Can generally lead to the wearing of some parts of the instrument
or cause spurious action. It is therefore recommended that the in-
strument be installed in a place where there are no vibrations. In
cases where this is impossible it is a good idea to take measures
to lessen the effects (elastic supports, installation with the switch
plunger of the microswitch positioned at right angles to the vibra-
tion plane).
1.4
TEMPERATURE
Due to the temperature of both the environment and the process
fluid, the temperature of the instrument could exceed the allowed
limits (normally from -40° to +60°C). Therefore, in case it does,
suitable measures (protection against heat radiation, fluid separa-
tors, cooling coils, heated lockers) must be taken. The process
fluid or its impurities must not however solidify in the instrument.
2

OPERATING PRINCIPLE

The pressure, acting on the sensitive element (diaphragm), deter-
mines its elastic deformation which is used to activate one or two
electric microswitches regulated at set point values. The micro-
switches are of the rapid release type with automatic rearm. When
the pressure moves away from the set values, returning towards
the normal values, the switch is rearmed. The dead band (gap be-
tween the set point value and the reset value) can be fixed or ad-
justable (letter R in the contact codes).
The versions with sensing element H or G are piston activated di-
aphragm instruments. The pressure, acting on a piston element,
generates a force which, applied to the diaphragm, causes an elas-
tic deformation.
3

MODEL CODE

See Annex 1
4

IDENTIFICATION PLATE AND MARKINGS

The instrument is fitted with a metal plate bearing all its functional
characteristics and in case of flameproof or intrinsic safety execu-
tion also the markings prescribed by standard IEC/EN 60079-0.
Fig.1 shows the plate mounted on flameproof instruments.
Fig. 1 - Flameproof instruments plate
1 Notified body that issued the type certificate and number of said
certificate.
2 CE marking and identification number of the notified body re-
sponsible for production surveillance.
3 Apparatus classification according to ATEX 2014/34/EU di-
rective.
4 Type of protection and ambient temperature limits of operation.
INSTRUCTION MANUAL
The following table gives the relationship between hazardous ar-
eas, Atex Categories and Equipment Protection Level (EPL) listed
on the flameproof instrument nameplate
Gas, vapours, fog Zone 0
Gas, vapours, fog Zone 1
Gas, vapours, fog Zone 2
Dust
Dust
Dust
5
Each microswitch is independent and can be adjusted by means
of a screw (for adjustment) to snap when the pressure reaches
(increasing or decreasing) the desired value (set point). The instru-
ment is usually supplied with the switches adjusted at the setting
range value nearest to zero (factory calibration). The instrument
is supplied with a label showing the set point calibration value. With
factory calibration the values are not indicated, as these are tem-
porary and will be modified with the definitive values. Prior to in-
stallation the instrument must be calibrated and the definitive cal-
ibration values written on the label.
If the instrument has been ordered with a specific calibration,
check the calibration values marked on the relevant label, prior to
installation.
The position of the adjustment screw is given in figure 2.
Fig. 2 - Electrical connections and adjustment screws
1- Microswitch 1 set point calibration screw
2- Microswitch 2 set point calibration screw
3- Electrical connection identification plate
4- Terminal block
Condition of the contacts at atmosphere pressure
Designation of the contacts:
C
NA - Normally open
NC - Normally closed
The effect that the direction of rotation of the adjustment screw has
is described on the label.
6
In order to proceed with the calibration and the periodical functional
verification of the instrument a suitable calibration circuit (Fig. 3)
and an adequate pressure source is required. The test instrument
should have a measurement range approximately equal to or
slightly wider than the pressure switch range and should have an
accuracy consistent with the accuracy required to calibrate the set
point.
Categories ac-
cording to
Hazardous area
2014/34/EU Di-
rective (ATEX)
1G
2G or 1G
3G, 2G or 1G
Zone 20 1D
Zone 21 2D or 1D
Zone 22 3D, 2D or 1D

SET POINT REGULATION

- Common

SET POIT CALIBRATION

NI-221WE
Rev. 5 12/16
EPL
Ga
Gb or Ga
Gc, Gb or Ga
Da
Db or Da
Dc, Db or Da
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