INSTRUCTION MANUAL
NI-205WE
Rev. 3 12/16
3 of 8
5 SET POINT REGULATION
Each microswitch is independent and can be regulated by
means of a screw (for adjustment to snap 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
alabel 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 label.
If the instrument has been ordered with a
specific
calibration
, check the calibration values marked on the
relevant label, prior to installation.
The position of the adjustment screws is given in figure 3.
Fig. 2 - Electrical connections and adjustment screws
1 - Microswitch 2 set point calibration screw
2 - Microswitch 1 set point calibration screw
3 - Terminal block
4 - Electrical connection identification plate
Microswitch electrical circuit: State of the contacts at zero
absolute pressure
Designation of the contacts:
C - common
NA - Normally open
NC - Normally closed
The effect that the direction of rotation of the adjustment
screws has is described on the label.
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 is required. 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.
Fig 4 - Calibration circuit
PS - Pressure switch
CA - Test pressure gauge for
absolute pressure
V1 - Inlet valve
V2 - Outlet valve
P - Absolute pressure source
6.1 PRELIMINARY OPERATIONS
6.1.1 Weatherproof pressure switches (Models APW)
Remove the blocking device fixed to the side of the
instrument case and the adjustment screw access
plate(fig. 59. Remove the cover by rotating it in an
anticlockwise direction.
Fig. 5 - Weatherproof pressure switch blocking and
plumbing device
a - Plumbing wire
b - Plumbing
c - Blocking nut
d - Blocking bracket
e - Adjustment screw access
plate
6.1.2 Flameproof pressure switches (Models APA)
CAUTION:
do not open the cover of flameproof pressure
switches (Models APA) when energized, in explosive
atmospheres.
Loosen the locking headless screw
situated on the cover
using a 1,5 hexagonal key then unscrew the cover (fig.6).
Remove the internal blocking device inserted on the
closure plugs and slide out the plugs.
Fig. 6 - Flameproof pressure switch blocking device
6.2 CALIBRATION CIRCUIT AND OPERATIONS
Prepare the control circuit as indicated in Fig.4.
The warning lamps should be connected to contact 1 or 2
in the NO or NC position according to the required contact
action.
Connection of C and NO terminals
• If the circuit is open at the working pressure, the switch
closes
the circuit as the pressure
increases
when the
desired value is reached.
• If the circuit is closed at the working pressure, the switch
opens
the circuit as the pressure
decreases
when the
desired value is reached.
Connection of C and NC terminals
•
If the circuit is closed at the working pressure, the switch
opens
the circuit as the pressure
increases
when the
desired value is reached.
• If the circuit is open at the working pressure, the switch
closes
the circuit as the pressure
decreases
when the
desired value is reached.
The pressure switch must be mounted in the normal
installation position, i.e. with the pressure connection
pointing downwards.
Avoid forcing the elastic support of the microswitch by
hand or with tools. This could affect the instrument
functioning.
CAUTION:
if the switch is of the kind with adjustable dead
band (letter R of contacts code) before proceeding with
the following operations it is necessary to proceed with
the adjustment of the dead band.
Increase the pressure in the circuit up to the desired set
point value for the first microswitch.
