INSTRUCTION MANUAL
NI-205WE
Rev. 3 12/16
4 of 8
Use a wide bladed screwdriver, as indicated on the
adhesive plate, until the relative lamp turns on (or turns
off).
- If the instrument is equipped with only one contact the
calibration is complete.
- If it is equipped with two contacts continue in the
following manner.
Vary the pressure until the desired set point value for the
second microswitch is reached (fig. 3).
Act on the adjustment screw of the second contact.
Repeat former operations on the first contact, then
operations on the second contact, until the required set
point precision is obtained. This is necessary due to the
reciprocal influence which the microswitches have on the
sensitive element of the instrument.
CAUTION:
if the two set point are different they must be
different for much of 5% of the adjustable span.
6.3 CHECK OF SET POINT
Generate the normal working pressure and wait the
pressure stabilisation. Vary the pressure into the circuit
and record the set point value. Write the set point values
on the adhesive label.
Note
: the repeatability should be checked verifying for
three times the set point (Pi) starting always from the
same pressure value (Pw). The pressure cycle should be
slowly to give the possibility to record the set point with
accuracy..
6.4 CALIBRATION CIRCUIT FOR INSTRUMENT
WITH ADJUSTABLE RANGE LESS TO 60 mbar
The calibration circuit used for the calibration of these
instruments must be:
- of big internal volume (5 liters or bigger) in order to
reduce the effect of volumetric variation (and therefore of
pressure) caused by the sensing element of the pressure
switch during the snap action.
- in a thermally stable place in order to guarantee stability
to the pressure inside the circuit used for the calibration.
Have to be considered that in a closed circuit with the
internal pressure equal to the atmospheric pressure, the
variation of temperature of 1°C causes in the circuit a
pressure variation of 3,4 mbar.
The maximum inlet pressure must not exceed the lesser
of overpressure allowed by the pressure switch and the
test gauge.
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 accuracy required to calibrate the set point.
For example APW10 range 0..16mbar the accuracy of the
test gauge must be ± 0,04 mbar to calibrate the set point
with an accuracy of ± 0,16 mbar (1% of the adjustable
span).
Fig. 6 – Calibration circuit for instrument with adjustable
range less than 60 mbar
1- Pressure switch
2- Test gauge
3- Inlet valve
4- Volumetric pump
5- Capacity
6- Outlet valve
6.5 ADJUSTMENT OF DEAD BAND (LETTER R ON
THE MODEL CODE)
The dead band can be adjusted only on the instrument is
equipped with a microswitch, which allows adjusting
(Letter R on the model code). Adjustment may be
obtained by rotating the wheel placed on the microswitch
(Fig. 7).
In order to carry out this operation it is advisable to use a
blade screwdriver.
Fig. 7 – Adjustment of dead band
Set point calibration screw
Dead band adjustment wheel
WARNING:
rotate the wheel without pushing too much
the blade against it.
The instrument is normally delivered adjusted on the
minmum value
of its range (factory calibration).
Calibration of dead band
The calibration of the dead band is obtained using the
following procedure:
1 - Raise pressure in the circuit until reaching the set
point and record its value (Pi).
2 - Reduce pressure in the circuit until reaching the reset
point and record its value (Pr).
3 - The difference Pi - Pr = Va represents the dead band
factory adjusted value.
4 - Rotate the adjustment wheel in the sense shown in
Fig. 6 placing the red notch in horizontal position
5 - Repeat operations 1 and 2 and measure the new dead
band Vb.
6 - By comparing the values Va and Vb approximately
determine the color of the wheel notch to be placed on
the mark.
7 - Place the notch and measure the obtained dead band.
8 - Proceed by successive approximations until reaching
the desired dead band value with enough accuracy.
9 - Then proceed with the set point calibration
Example:
The dead band increase corresponding to the
rotation from A to B is given by: Vb - Va =I
The desired dead band V will be approximately in the
position indicated by the value
I
V
K
which
expresses:
-
By units, the wheel notches (1=one black notch,
2=one red notch, 3=one yellow notch, 4=one blue
notch, 5=one green notch, 6=two black notches).
-
By decimal digits, the percentage middle position
between the located notch (of units) and the following
one.
6.6 FINAL OPERATIONS
Disconnect the instrument from the calibration circuit.
6.6.1 Weatherproof pressure switches (Models APW)
Take the cover, ensure that the sealing gasket is correctly
fitted into its seat, and insert the cover onto the case, with
the blocking gap positioned in correspondence to the
blocking bracket. Turn the cover clockwise closing it
tightly. Mount the adjustment screw access plate, then the
blocking device as in Fig.4.
