WIKA MAB User Manual
NI-221E
INSTRUCTION MANUAL
Rev. 1 11/02
DIAPHRAGM PRESSURE SWITCHES
WEATHERPROOF:SERIES MW EXPLOSIONPROOF: SERIES MA
Models: MW-MWH Models: MA-MAH-MAG
A = pressure attachment
B = cable entry
WEIGHT 1,8 kg dimensions in mm WEIGHT 3,2 kg dimensions in mm
NOTE: dimensions and weights are not binding unless released on certified drawings.
CAUTION
• Before installing, using or carrying out maintenance on the instrument it is necessary to read and understand the
indications given in the attached Instruction Manual.
• The instrument must only be installed and maintained by qualified personnel.
• INSTALLATION IS TO BE CARRIED OUT ONLY AFTER CHECKING THAT INSTRUMENT CHARACTERISTICS
ARE CONSISTENT WITH PROCESS AND PLANT REQUIREMENTS.
• The functional features of the instrument and its degree of protection are shown on the identification plate fixed to the
case.
CONTENTS:
1
GENERAL NOTES
2 OPERATING PRINCIPLE
3 IDENTIFICATION PLATE AND MARKINGS
4 SET POINT REGULATION
5 SET POINT CALIBRATION
6 MOUNTING AND CONNECTIONS
7 INSTRUMENT PLUMBING
8 PUTTING INTO OPERATION
9 FUNCTIONAL VERIFICATION
10 TROUBLESHOOTING
11 STOPPING AND DISMOUNTING
12 DEMOLITION
SAFETY INSTRUCTIONS FOR USE IN HAZARDOUS ATMOSPHERES.
RECOMMENDATIONS FOR PRESSURE SWITCH SAFE USE.
A = pressure attachment
B = cable entry
RELATED DOCUMENT
To authentified document with certificate
N° CESI 02 ATEX 144
All data, statements and recommendations supplied with this manual are based on information believed by us to be
reliable. As the conditions of effective use are beyond our control, our products are sold under the condition that the
user himself evaluates such conditions before following our recommendations for the purpose or use foreseen by him.
The present document is the property of ETTORE CELLA SPA and may not be reproduced in any form, nor used for
any purpose other than that for which it is supplied.
INSTRUCTION MANUAL
1 GENERAL NOTES
1.1 FOREWORD
The wrong choice of a series or a model, as well as the
incorrect installation, 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 tolerated provided they remain within the limits stated
in the instrument features (vacuum or proof pressure).
Continuous pressures exceeding the working range can
be applied to the instrument provided they are clearly
stated in the instrument features. The current and voltage
values stated in the technical specifications and ratings
must not be exceeded. Transitory overages can have a
destructive effect on the switch.
1.3 MECHANICAL VIBRATION
Can generally lead to the wearing of some parts of the
instrument or cause false actuation. It is therefore recommended that the instrument 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 peg of the microswitch positioned at right angles to the vibration 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 -20° to +70°C).
Therefore, in case it does, suitable measures (protection
against heat radiation, fluid separators, cooling coils,
heated lockers) must be taken.
2 OPERATING PRINCIPLE
• The pressure, acting on the sensitive element (dia-
phragm), determines its elastic deformation which is used
to activate one or two electric microswitches regulated at
set point values. The microswitches 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 differential gap
(difference between the set point value and the reset
value) can be set or adjustable (letter R in the contact
codes).
• Piston activated diaphragm instruments (MWH - MAH)
differ from the former as the pressure, acting on the piston
Fig. 2 - Electrical connections and adjustment screws
NI-221E
Rev. 1 11/02
element, generates a force which, applied to the diaphragm, causes an elastic deformation. This deformation
is then used as in the previous case, to activate one or two
microswitches.
3 IDENTIFICATION PLATE AND MARKINGS
The instrument is fitted with a metal plate bearing all its
functional characteristics and – in case of explosionproof
execution (Series MA) – also the markings prescribed by
standard CEI EN 50014. Fig.1 shows the plate mounted
on explosionproof instruments.
Fig. 1 - Explosionproof instruments plate
1 CE marking and identification number of the notified body
responsible for production surveillance.
2 Apparatus classification according to ATEX 949 CE directive.
3 Type of protection and ambient temperature limits of opera-
tion.
4 Notified body that issued the type certificate and number of
said certificate.
4 SET POINT REGULATION
Each microswitch is independent and can be regulated by
means of a screw (for adjustment) in such a way that it is
released when the pressure reaches (increasing or decreasing) the desired value (set point). The instrument is
usually supplied with the switches set at the setting range
value nearest to zero (factory calibration). The instrument is supplied with an adhesive rating plate showing the
set point calibration value. With factory calibration the
values are not indicated on the ratings, as these are temporary and will be modified with the definitive values. Prior
to installation the instrument must be calibrated and the
definitive calibration values written on the adhesive rating
plate using a suitable indelible ink pen.
1- Microswitch 1 set point
calibration screw
2- Microswitch 2 set point
calibration screw
3- Electrical connection identifi-
cation plate
4- Terminal block
Designation of the contacts:
C - Common
NA - Normally open
NC - Normally closed
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