WIKA MAB - Manual (Page 2)

INSTRUCTION MANUAL
NI-221E
Rev. 1 11/02
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 in-
strument 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 occasion-
ally 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 recom-
mended 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 mi-
croswitch 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 re-
lease 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
element, generates a force which, applied to the dia-
phragm, 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 de-
creasing) 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 instru-
ment 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 tem-
porary 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.
Fig. 2 - Electrical connections and adjustment screws
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