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
INSTRUCTION MANUAL
6.1 PRELIMINARY OPERATIONS
Slide up the adjustment cover (Fig. 2, 1).
6.2 CALIBRATION CIRCUIT AND OPERATIONS
Prepare the control circuit as indicated in Fig.4.
The warning lamps should be connected to the terminals NA or
NC according to the required contact action.
If the instrument is equipped with two contacts, remember that
they are released simultaneously but within the specification
tolerance.
Connection between C and NA
• If the circuit is open at the working pressure, the instrument
closes the circuit when the set point is reached with pressure on
rise (closure on rise).
• If the circuit is closed at the working pressure, the instrument
opens the circuit when the set point is reached with pressure on
fall (opening on fall).
Connection between C and NC
• If the circuit is closed at the working pressure, the instrument
opens the circuit when the set point is reached with pressure on
rise (opening on rise).
• If the circuit is open at the working pressure, the instrument
closes the circuit when the set point is reached with pressure on
fall (closure on fall).
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 precision
required to calibrate the set point.
The pressure switch must be kept in the normal installation
position, i.e. with the pressure connection downwards.
Modify the pressure in the circuit up to the desired microswitch set
point value.
Turn the adjusting bush using the adjustment rod until the relative
lamp turns on (or turns off); then turn it in the opposite direction
until the lamp turns off (or on). Slowly turn the bush again until the
lamp turns on (or off).
Fig. 4. Calibration circuit
NI-290E
Rev. 0 01/05
8 - MOUNTING AND CONNECTION S
8.1 MOUNTING
Mount the instrument directly on the pressure tap (Fig. 11) or on a
surface, through either a manifold (Fig.9) or a junction box (Fig.
10). If the optional bracket for surface or pipe mounting is used,
refer to NI-292E. The chosen position must be such that possible
shocks or temperature changes remain within tolerable limits.
With gas or vapour process fluid, the instrument must be
positioned higher than the pressure tap. With a liquid process
fluid, the instrument can be positioned higher or lower,
indifferently. In this case, during set point calibration the negative
or positive head must be taken into account.
8.2 PRESSURE CONNECTION
For a correct surface mounting (Fig. 9 and 10) proceed as follows.
Mount a shut-off valve with drain (root valve) on the pressure tap
to allow the instrument to be excluded and the connection tubing
to be drained. It is recommended that said valve has a capstanblocking device aimed at preventing it from being activated
casually and without authorisation.
Mount a service valve near the instrument to permit possible
functional verification on site. It is recommended that the service
valve is closed with a plug to prevent the outlet of the process
fluid caused by the incorrect use of said valve.
Mount a three piece joint onto the threaded attachment of the
instrument to permit the easy mounting or removal of the
instrument itself.
CAUTION: the pressure connection is to be tightened
applyIng the wrench ONLY on the hex of the pressure
attachment, NOT to the hex of the conduit connection, which
may cause the instrument NOT to work (Fig.5).
Fig. 5. Pressure connection
PS - Pressure switch
CA - Test gauge
V1 - Inlet valve
V2 - Discharge valve
P - Pressure source
Check the calibration value (varying the pressure in the circuit
accordingly) and register it, using a pen with indelible ink, on the
adhesive label.
Test fluid :
- air for P ≤ 10 bar
- water for P > 10 bar
6.3 FINAL OPERATIONS
Disconnect the instrument from the calibration circuit.
Close the adjustment slot by sliding down the slot cover (Fig. 2,
1), then seal with lead the instrument.
Mount on pressure connection the protecting cap supplied with
the instrument. It should be definitively removed only during the
connection steps.
7 - INSTRUMENT PLUMBING
The plumbing (see Fig. 2), aimed as a guarantee against possible
tampering of the calibration, can be carried out using a flexible
steel wire (2), 1 mm
groove purposely provided.
2
in section, wound up around the case in the
Make use of a flexible tubing between instrument and pressure
tap so that, due to temperature changes, no mechanical stress be
applied to instrument connection.
Make sure that all the pressure junctions are leakproof. It is
important that there are no leakages in the circuit.
Close the root valve, the relative drain device and the service
valve fitted with safety plug.
8.3 ELECTRICAL CONNECTIONS
It is recommended to carry out the electrical connections
according to the applicable standards. In case of explosionproof
instruments (Series PXA and PXN) see also the standards EN60079-14 and EN 50281-1-2
The following mounting arrangements are possible.
8.3.1 MOUNTING WITH CABLE LOOSE
Run the cable so that it cannot be easily damaged (e.g. due to too
narrow bends, heat sources) and strain it.
Mount, if provided, the external ground device on the electrical
connection of the instrument. This device is to be threaded on,
while holding the electrical connection steady with a 27 mm
wrench on hex, until it reaches the bottom of the thread (Fig. 6).
INSTRUCTION MANUAL
The external ground screw is obligatory for explosionproof
constructions.
Fig. 6. Mounting of ground device
8.3.2 MOUNTING WITH CABLE PROTECTED BY
FLEXIBLE TUBING
Mount, if provided, the external ground device on the electrical
connection of the instrument. This device is to be threaded on,
while holding the electrical connection steady with a 27 mm
wrench on hex, until it reaches the bottom of the thread (Fig. 6)..
The external ground screw is obligatory for explosionproof
constructions.
If the flexible tubing is fitted with a male thread, apply a sleeve to
the electrical connection.
CAUTION: the sleeve is to be threaded on while holding the
electrical connection steady with a 27 mm wrench on hex (Fig.7) .
Fig. 7. Mounting of adaptors
DO NOT TURN
NI-290E
Rev. 0 01/05
Terminals are identified as follows:
Identification No. Function Micro No.
1 Common
2 Normally Open
3 Normally Closed
4 Common
5 Normally Open
6 Normally Closed
Mounting with cable protected is to be carried out so as to
prevent possibile condensate from entering the junction box.
The junction box is to be surface mounted using the bracket
suppiled with it.
CAUTION: accessories used for installation have to be certified
according to standards EN 50014, 50018, EN 50281-1-1 and
guarantee the degree of protection of the instrument (IP65)
CAUTION: cable entries not used must be plugged and sealed
with the plugs provided so as to prevent raining water or other
from entering the junction box. In case of explosionproof
instruments these plugs, if not correctly mounted and
blocked to prevent their removal, do NOT guarantee the
mode of protection EEx-d. Furthermore, in order to guarantee
the degree of protection IP65 and the non-loosening of blocking
joint or packing gland, it is prescribed to seal the threads of
connection with the same anaerobic sealant used for the plugs.
For instance, a sealant like Loctite ® 648 can be applied on the
thread of plugs, blocking joint or packing gland before screwing
them on the box.
1
2
DO NOT TURN
8.3.3 MOUNTING WITH CABLE PROTECTED BY
METAL TUBING
CAUTION: mounting with cable protected by metal tubing is to be
carried out avoiding any torque on the electrical connection while
assembling the various fittings (Fig. 7).
In order to make easier the instrument removal for check and
calibration it is advisable to apply on the instrument a junction box
provided with terminals.
CAUTION: accessories used for installation have to be certified
according to standards EN 50014, 50018, EN 50281-1-1 and
guarantee the degree of protection of the instrument (IP65).
8.3.4 MOUNTING WITH INSTRUMENT FITTED WITH
JUNCTION BOX
Models fitted with junction box feature three cable entries, threeor six-terminals block with terminals identification plate, internal
and external grounding connections.
8.4 WIRING
The cable used for electric wirIng has a 7 mm OD silicone sheat
for one contact models, 8 mm OD for two contact models. Each
wire has a section of 0,5 mm
Wires ends are factory tinned. The colour of insulator defines the
contact function (see Fig. 3 and stampings on slot cover).
Before starting wiring, check that electric lines are not
powered.
The instrument is to be grounded according to applicable
electrical codes. Make use of the internal yellow-green wire and,
if the cable is not protected by metal tubing, connect the external
screw of the groundig device supplied with the instrument.
Should the instrument be fitted with junction box, make sure that
no deposits or wire ends remain inside the box. The wiring
completed, put the cover on and tighten it.
2
(20 AWG) and is silicone insulated.
8.5 SPECIAL NOTE FOR THE INSTALLATION OF
PRESSURE SWITCHES CATEGORY 1 / 2 G AND 1 / 2
D
Explosionproof pressure switches (Series PXA) may be installed
on process requiring apparatus of Group II Category 1 in an area
requiring apparatus of Group II Category 2 (see Fig. 8).
INSTRUCTION MANUAL
Fig. 8. Instruments installation
Group II Cat 1/2G Group II Cat 1/2D
The instrument starts operating as soon as the root valve is
opened. Any possible drainage of the connection tubing can be
carried out by removing the safety plug and opening the service
valve with the necessary caution.
In case of explosionproof instruments (Series PXA and PXN),
initial inspections are to be carried out according to customer
procedures and at least in accordance with Standards EN-6007917 and EN-50281-1-2.
NI-290E
Rev. 0 01/05
10 - FUNCTIONAL VERIFICATION
It will be carried out according to customer control procedures.
Explosionproof instruments (Series PXA, PXN) installed in
hazardous areas due to the presence of inflammable dusts should
be periodically cleaned externally to avoid dust accumulation.
8.6 SPECIAL NOTE FOR THE INSTALLATION OF
PRESSURE SWITCHES CATEGORY 3GD MODE OF
PROTECTION EEx - nC
Explosionproof instruments Series PXN are to be installed using
electric accessories prescribed for this execution. For instance,
junction boxes are to be suitable for mode of protection n. Apply
to standards EN-50021 for any construction detail and to EN60079-14, EN-50281-1-2 for installation.
9 - PUTTING INTO OPERATION
As the signal transmitted by the instrument is used in a complex
system, it is necessary that the means of putting it into operation
are established by those in charge of the plant.
Instruments Series PXS may be checked on site if installation has
been made according to Fig. 9 to 12.
Instruments Series PXA, PXN may be checked on site but if
testing equipments are suitable for the environment and electric
supply is off.
Otherwise it is necessary to stop them working, remove them and
carry out checks in a test room.
The verification consists in checking the calibration value and
adjusting it if required (see §5).
In case of explosionproof instruments (Series PXA and PXN)
inspections of the electrical installation are to be carried out also
according to customer procedures and at least in accordance with
Standards EN-60079-17, EN-50281-1-1.
11 - TROUBLE SHOOTING
IMPORTANT NOTE: operations involving replacement of essential components must be carried out at our workshop, especially
for instruments with explosionproof certificate; this is to guarantee the user the total and correct restoration of the product
original characteristics.
MALFUNCTION PROBABLE CAUSE REMEDY
Permanent deformation of the sensitive element
Set point shift
Slow response
No actuation or
undue actuation
Undue actuation
due to fatigue or excess over-ranges.
Variation of the elastic features of the sensitive
element due to its chemical corrosion.
Clogged or obstructed connecting line.
Root valve partially closed.
Too viscous fluid.
Root valve closed.
Microswitch contacts damaged.
Loosened electrical joints.
Interrupted or short-circuited line.
Accidental shocks. Modify mounting.
12 - STOPPING AND DISMOUNTING
Before starting the following operations, ensure that plant and
equipments have been put in conditions allowing to carry out
them safely.
With reference to Fig 10.
Remove the power supply (signal) from the electric line. Close
the root valve (10) and open drain. Remove plug (5), open valve
(6) and wait for process fluid to drain out.
Do not dispose of the process fluid into the environment, if this
can cause pollution or damage to people.
Unscrew the three-piece joints (11) and (3) (electric cable tubing).
Remove cover from junction box and disconnect wires from
terminals and grounding screws. Remove the screws fixing the
box to the panel (or pipe) and remove the instrument taking care
to slide electric conductors out from the case.
Replace the cover on the box. Insulate and protect the
conductors remaining on the plant. Temporarily plug the tubing
(7). In case of explosionproof instruments (Series PXA, PXN) it is
recommended to follow - at least – the Standards EN-60079-17
and EN-50281-1-2 for the withdrawal from service of electrical
apparatus.
13 - DEMOLITION
The instruments are mainly made of stainless steel and
aluminium and therefore, once the electrical parts have been
dismounted and the parts coming into contact with fluids which
could be harmful
to people or to environment have been properly dealt with, they
can be scrapped.
Recalibrate or replace the sensitive element.
Recalibrate or replace the sensitive element with
another made of a suitable material. If necessary
apply fluid separator.
Check and clean line.
Open the valve.
Provide instrument with suitable fluid separator.
Open the valve.
Replace instrument.
Check all electrical joints.
Check conditions of the electric line.
INSTRUCTION MANUAL
Fig. 9. Example of surface mounting Fig. 10. Example of surface mounting
WEATHERPROOF OR EXPLOSIONPROOF
15
14
NI-290E
Rev. 0 01/05
Fig. 11. Example of direct mounting Fig. 12. Example of mounting
14
1 – Elbow fitting
2 – Blocking joint
3 – Three-piece joint
4 – Adaptor
5 – Drain plug
6 – Service valve
7 – Tubing
8 – Three-piece joint
9 – Process piping
10 – Root valve with drain
11 – Three-piece joint
12 – Tee fitting
13 – Manifold
14 – Ground ring
15 – Sleeve
ETTORE CELLA SPA Viale de Gasperi, 48 - Casella Postale (P.O. Box) 96 - I 20010 Bareggio (MILANO) ITALY
Telefoni +39 029036.1146/7 - 029036.1237/41 - FAX +39 029036.1331 Email: CELLA@ECELLASPA.COM
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