WIKA BWX - Manual (Page 2)

INSTRUCTION MANUAL
NI-222E
Rev. 1 12/02
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
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 occa-
sionally tolerated provided they remain within the limits
stated in the instrument features (vacuum or proof pres-
sure). 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 overranges
can have a destructive effect on the switch.
1.3 MECHANICAL VIBRATIONS
Can generally lead to the wearing of some parts of the
instrument or cause false actuation. It is therefore rec-
ommended 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, etc.).
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 (Bourdon
tube), 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).
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 BAX) – also the markings prescribed
by standard CEI EN 50014. Fig. 2 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 94/9 CE direc-
tive.
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 cali-
bration).
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 defini-
tive values.
Prior to installation the instrument must be calibrated
and the definitive calibration values written on the adhe-
sive rating plate using a suitable indelible ink pen.
If the instrument has been ordered with a specific cali-
bration, it is a good rule to check the calibration values
marked on the relevant adhesive label, prior to installa-
tion.
The position of the adjustment screws is given in figure
The effect that the direction of rotation of the adjustment
screws has is described on the adhesive plate.