WIKA PXA User Manual

INSTRUCTION MANUAL

NI-290E

Rev. 0 01/05

PRESSURE SWITCHES SERIES PXS, PXN, PXA

WEATHERPROOF (Series PXS) AND EXPLOSIONPROOF (Series PXA, PXN)

INSTRUMENT STANDARD INSTRUMENT WITH JUNCTION BOX

A = Pressure connection B = Cable entry A = Pressure connection B = Cable entry

WEIGHT 0,3 kg Dimensions in mm WEIGHT 1kg 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:

GENERAL

1 ­2 - OPERATING PRINCIPLE
3 - NAMEPLATE AND MARKINGS
4 - SPECIAL CONDITIONS FOR SAFE USE (X)
5 - SET POINT ADJUSTMENT
6 - SET POINT CALIBRATION
7 - INSTRUMENT PLUMBING
8 - MOUNTING AND CONNECTION S
9 - PUTTING INTO OPERATION
10 - FUNCTIONAL VERIFICATION
11 - TROUBLE SHOOTING
12 - STOPPING AND DISMOUNTING
13 - DEMOLITION

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 for which it is supplied.

SAFETY INSTRUCTIONS FOR USE IN EXPLOSIVE ATMOSPHERES

RECOMMENDATIONS FOR THE SAFE USE OF THE INSTRUMENT

DOCUMENT CORRELATED

to document authenticated with certificates

N° CESI 05 ATEX 002X

N° CESI 05 ATEX 003

INSTRUCTION MANUAL

1 - GENERAL

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 follow the indications given in this manual can cause damage
to the instrument, the environment and persons.

1.2 ALLOWED OVERRANGES

Pressures exceeding the working range can be occasionally
tolerated provided they remain within the limits stated for the
instrument (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 data plate must not be exceeded: transitory
overranges can have a destructive effect on the switch.

1.3 TEMPERATURES

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°C to +85°C). Therefore, in case it does,
suitable measures (protection against heat radiation, fluid
separators, cooling coils, heated lockers), aimed at limiting the
value, must be taken.

2 - OPERATING PRINCIPLE

A pressure-tight diaphragm (or an O-ring sealed piston) applies a
force to a stiff disc. This force is directly proportional to the
pressure value and is contrasted by an helicoidal spring charged
by a suitable bush. When the force balance point is exceeded, the
stiff disc shifts and, by means of a rigid rod, actuates one or two
simultaneous release electric microswitches. The
microswitches are of the snap acting type with automatic reset.
When the pressure moves away from the set values, returning
towards the normal values, the switch is reset.

3 - NAMEPLATE AND MARKINGS

The instrument is fitted with a metal plate bearing all its functional
characteristics and – in case of explosionproof execution (Series
PXA and PXN) – also the markings prescribed by standard EN
50014 and EN 50281-1-1. Fig. 1 shows the nameplate mounted
on explosionproof instruments.

Fig. 1. Nameplate, explosionproof instruments

1 CE marking and identification number of the notified body

responsible for production surveillance.
2 Apparatus classification according to ATEX 94/9 CE directive.
3 Notified body that issued the type certificate and number of said

certificate.
4 Mode of protection and operating ambient temperature limits.

4 - SPECIAL CONDITIONS FOR SAFE USE (X)

Explosionproof instruments (Series PXA and PXN) installed
without a junction box require an electric connection suitable for
the mode of protection choosen at the free end of the cable (see
Point 8). Should the instrument be installed on a dangerous
process fluid (Zone 0), check wetted materials compatibility.

NI-290E

Rev. 0 01/05

5 - SET POINT ADJUSTMENT

The charge of the helicoidal spring can be regulated by means of
the bush (for adjustment) in such a way that the switch is released
when the pressure reaches (either 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
label showing the set point calibration value. With factory
calibration the values are not indicated on the label 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 label using a suitable indelible ink
pen.

If the instrument has been ordered with a specific calibration, it
is a good rule to check the calibration values marked on the
relevant adhesive label, prior to installation.

The position of the adjusting bush is given in Fig. 2.

Fig. 2. Adjusting bush and plumbing

c Adjustment

slot cover

d Stainless steel

wire

e Sealing lead
f Adjusting

bush

The effect of the sense of rotation of the adjusting bush is shown
on the slot cover. Rotate the bush by inserting a 3mm dia. rod or
drill into the holes on the bush itself.

6 - SET POINT CALIBRATION

In order to proceed with the calibration and the periodical
functional verification of the instrument a suitable calibration
circuit (Fig. 4) and an adequate pressure source are required.
Wiring is to be carried out as shown in Fig. 3 and on the slot
cover.

Fig. 3. Electric wiring

GDN - Ground internal : leadwire yellow/green
C - Common : leadwire brown
NA - Normally open : leadwire blue
NC - Normally closed : leadwire black
C - Common : leadwire grey
NA - Normally open : leadwire red
NC - Normally closed : leadwire white

Microswitch internal wiring and contacts status at atmospheric
pressure

Micro 1

Micro 2

C - Common
NA - Normally open
NC - Normally closed