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below to the 50% of L.E.L. of the applied gas.
To apply the Span gas it is necessary to convey
to the transmitter sensor the certified gas from
the cylinder as shown in the following figure.
Trasmitter
FULL-SCALE
Adapter
GAUGE
min. 100Pa
RESOLUTION
1Pa
Fig. 7: How to convey the gas to the transmitter
for the inspection or calibration operations.
The gauge is necessary to check that an
excessive extra pressure is not created on the
sensor, because this condition can lead to a
wrong concentration reading.
The transmitter must have been operative for at
least 48 hours in clean air and must be set in its
normal functioning setting.
Regulate the gas flux towards the sensor until
on the gauge is displayed the value of 10 Pa
(about 0,2 l/min.) which will have to remain
steady for the entire inspection.
From the moment in which the gas reaches the
sensor, the drive voltage of the current loop will
gradually rise up to stabilize, after about 5
minutes, around a value.
The easiest way to measure the current in the
output loop, in order to perform the inspection, is
to 'cut' this loop and insert a handheld multimeter
in series, as shown in the following figure.
+Vin S Gnd
12-24V
In Gnd
4..20mA
Control
set in mA (with two
Unit
decimal resolution
Fig. 8: Multimeter
connection
measuring during the Zero and Span
check.
──────────────────────────────────
VERIFICATION - Combustible and toxic
gases
──────────────────────────────────
Zero signal test (Combustible gases)
When the Zero gas is applied (clean air) the
output current measured with the multimeter
must be 4.0mA ±0.2mA. If the measured value
is not inside this range, a calibration is
necessary to reset the correct value (see
further). For versions with digital output on the
bus, the concentration value read by the unit
must be zero.
Span signal test (Combustible and toxic
gases)
When the Span gas reaches the sensor the
output current will rise gradually until stabilizing
SY-N000000SE 034969 310720
around a value (after about 5 minutes).
If the 4..20mA current output is used, at this
point it is necessary to note the measured
current value on the multimeter and, referring to
the table or to the concentration-current graph
of Fig. 2, 3 and 4 (depending on the full-scale
and
on
Flowmeter
combustible)
concentration value.
Instead, if the Modbus® output is used, it is
necessary to note the value (directly in ppm or
% of L.E.L.) displayed on the unit connected to
the transmitter.
In case the measured value is not correct it is
necessary to calibrate the Span as described in
the next section.
If the result of the previous checks is positive
then it is not necessary to proceed with the
calibration.
──────────────────────────────────
CALIBRATION - Overview
──────────────────────────────────
By the term 'calibration' it is meant the
procedure that must be performed on the
transmitter, possibly with the help of a tool,
aimed to bring back the output signal inside the
precision declared every time it is necessary.
A certain output current signal shifting is to be
considered inevitable, this being caused by
small drifts of the sensor itself, both for Zero and
Span.
The calibration of the transmitter is made
applying on the transmitter a sample gas which
concentration is known and certified and
regulating, through the appropriate controls
placed inside the transmitter, the output signals.
In detail, the procedure is articulated in the
following points:
Applying the Zero gas
Calibration of the Zero signal
Applying the Span gas
Calibration of the Span signal
Application of the Zero gas (Combustible
Gases)
Proceed as described in the "VERIFICATION"
paragraph.
Application of the Span gas (Combustible
and toxic gases)
Proceed as described in the "VERIFICATION"
paragraph.
WARNING
The
complete
+
implies the calibration of both of
-
parameters (first 'Zero' and then 'Span')
exactly in this order.
The transmitter must be operative for at
least 48 hours in clean air and must be
Multimeter
placed
operational standard.
──────────────────────────────────
digits).
CALIBRATION - Combustible gases
EG. --,-- mA.
──────────────────────────────────
for
current
To perform this procedure, a multimeter in
current mode is needed and it has to have at
least 2 decimal resolution digits to guarantee
the appropriate precision on the measure, see
figure 8.
Calibration of the Zero signal (Combustible
gases):
With the transmitter in clean air, rotate the
'ZERO' trimmer (see Fig.
clockwise direction, until the current stops at
a minimum value (about 4.00mA), then turn
the trimmer in clockwise direction until the
value rises up a little bit (eg: 4.10mA), then
turn slowly the trimmer in anti-clockwise
direction until bringing the current as close as
possible to the minimum value (eg: 4.00mA)
without exceeding this value.
This operation is the same for any version of
the transmitter, independently from the type
of output (analog or digital).
the
gas
classification,
toxic
convert
in
a
correspondent
calibration
necessarily
in
its
normal
position
9a) in anti-
Pag. 14/32
SPAN
or
Fig. 9a: Position of Zero and Span controls on
the sensor for combustibles gases.
WARNING
The regulation compels to have a precise
tuning for the minimum value (eg.: 4.00mA)
otherwise there will be an offset error.
Calibration of the Span gas (Combustible
gases):
Apply the Span gas as suggested in
paragraph 'Application of the Span gas
(Combustibles and toxic gases)' respecting
the stabilization time of at least 5 minutes.
Calculate, according to the following formula,
the calibration Span current:
Or:
Where:
F.S.:
Full-scale of the transmitter in % L.I.E.
Bottle concentration (%
Concentration of the sample gas applied to the
V
detector (in %
/
). This data can be found on the
V
certificate of the cylinder.
V
Target gas L.E.L. (%
/
):
V
Lower explosion limit of the gas test. This data can
be found on the EN60079-20-1 standard.
Bottle concentration (% L.E.L.):
Value of the sample gas applied to the detector
expressed in % of L.E.L. This data can be found
on the certificate of the cylinder.
Regulate
the
'SPAN'
multimeter shows a current equal to the one
calculated with the formulas. If the operation
is not successful at the first try, repeat the
procedure again, putting the sensor in clean
air and powered for at least 10 minutes.
the
Verify that on the unit the concentration value
(in % L.E.L.) measured by the related
transmitter, is equal to the value of the gas
used for the inspection with en error margin
equal to ±2 %.
and
Place
back
the
cover
checking the tightness of the closure.
──────────────────────────────────
CALIBRATION - Toxic gases
──────────────────────────────────
To perform this procedure, a multimeter in
current mode is needed and it has to have at
least 2 decimal resolution digits to guarantee
the appropriate precision on the measure, see
figure 8.
Zero signal calibration (Toxic gases):
With this kind of transmitters it is not necessary
to regulate the 'ZERO' signal.
Span signal calibration (Toxic gases):
Apply the Span gas as suggested in the
'Application
of
(Combustibles and toxic gases)' paragraph
respecting the stabilization time of at least 5
minutes.
Calculate, according to the following formula,
the calibration Span current:
ZERO
V
/
):
V
value
until
the
and
screw
it,
the
Span
gas
ENGLISH
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