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SX01 Schematic ( PDF Datasheet ) - Sensym

Teilenummer SX01
Beschreibung (SX01 / SX05) Pressure Sensor
Hersteller Sensym
Logo Sensym Logo 




Gesamt 10 Seiten
SX01 Datasheet, Funktion
SX Series
Pressure sensors
FEATURES
· 0...1 to 0...300 psi
· Absolute, differential
and gage devices
· High impedance bridge
· Low power consumption
for battery operation
www.DataSheet4U.com
APPLICATIONS
· Industrial controls
· Pneumatic controls
· Medical instrumentation
· Barometry
EQUIVALENT CIRCUIT
Vs
+
Output
-
Button sensor or "N" package
Vs
-
Output
+
TO can or DIP package
March 2004 / 052
GENERAL DESCRIPTION
The SX series of pressure sensors
provides the most cost effective
method of measuring pressures up
to 300 psi. These sensors were speci-
fically designed to be used with
non-corrosive and non-ionic media,
such as air and dry gases. Convenient
pressure ranges are available to
measure differential, gage and
absolute pressures from 0 to 1 psi
(SX01) up to 0 to 300 psi (SX7300D).
The absolute (A) devices have an in-
ternal vacuum reference and an output
voltage proportional to absolute
pressure. The differential (D) devices
allow application of pressure to either
side of the diaphragm and can be
used for gage or differential pressure
measurements.
However, 300 psi (SX7300D) can be
applied to pressure port P2 only.
Pressure port P1 is able to handle
operating pressures up to 150 psionly.
This product is packaged either in
SenSym's standard low cost chip
carrier "button" package, a plastic
ported "N" package, a metal TO can
package or a dual inline package (DIP).
All packages are designed for appli-
cations where the sensing element is
to be integral to the OEM equipment.
Scale:
1 cm
½ inch
These packages can be o-ring sealed,
epoxied, and/or clamped onto a
pressure fitting. A closed bridge 4-pin
SIP configuration is provided for elec-
trical connection to the button or "N"
package. The TO can offers a 5-pin
open bridge configuration.
Because of its high-impedance
bridge, the SX series is ideal for por-
table and low power or battery opera-
ted systems. Due to its low noise, the
SX is an excellent choice for medical
and low pressure measurements.
ELECTRICAL CONNECTION
Button sensor
GND 1
out + 2
+VS 3
out - 4
P1
Bottom view (open bridge)
GND
Out-
NC
Out+
781
62
5 43
NC
+Vs
+Vs
P2 vent hole
for gage
devices only
NC
+Vs P2
+Vs 4
1 out + out -
GND GND
out - out +
1
P1
+Vs out + 1
GND P1
4 +Vs out -
P2
+Vs
4 +Vs
vent hole
SXxxxGD2 DIP
SXxxxAD2
The polarity indicated is for pressure applied to:
SX...
: P1 (forward gage)
SX...AS/GSO : P1 (forward gage)
SX...AD2
: P1 (forward gage)
SX...GD2
: P2 (backward gage)
SX...DD4
: P2 (backward gage)
SXxxxD4 DIP
1/10
http://www.sensortechnics.com






SX01 Datasheet, Funktion
SX Series
Pressure sensors
APPLICATION INFORMATION (cont.)
a) VB=VS-4φ
φ
( )b) VB
( ) ( )VB
=
φ
VS -4
φ
( )c)
φ
φ
= -2500 ppm/°C for silicon diodes
www.DataSheet4U.com Figure II. Equations
For example, solving equation (b) for VB/
VBwhen
VS = 6.0 V
φ = 0.7 V
Yields:
V• B = 2188 ppm/°C
VB
Since the sensor’s span changes with tem-
perature at -2150 ppm/°C, this technique will
typically result in an overall negative TC of
38 ppm/C. This error is acceptable in most
applications.
For operation with V S above 6V, it is recom-
mended to use the transistor or constant
current compensation technique.
2. Transistor compensation network
Figure III uses a single transistor to simulate
a diode string, with the equations as shown.
The values shown in Table I were found to
give excellent results over 0°C to 70°C.
Again, if precision temperature compen-
sation is required for each device, the fixed
value resistors shown for R1 in Table I can
be replaced by a 3.24k resistor in series with
a 1k pot. Then, each devices temperature
compensation can be individually adjusted.
Figure III. Transistor/Resistor
span TC compensation
6/10
a) VB = VS - α φ
( ) ( ) (
VB
b) VB
=-
φ
φ
x
VS
c) α
=
1
+
R1
R2
( )
d) φ
φ
= -2500 ppm/°C
φ
α)
-α
Table I. Selected R values vs V S for
figure III
VS R1 ()
5V 3.32k
9V 4.02k
12V 4.22k
R2 ()
1.43k
806
604
3. Constant current excitation
(Figure IV)
The circuits shown in Figures II and III,
although simple and inexpensive, have one
drawback in that the voltage across the
bridge is determined by the compensation
network. That is, the compensation network
is determined and what voltage is “leftover"
is across the bridge. The circuit of Figure
IV solves this problem and allows the bridge
voltage to be independently selected. In
Figure IV, the bridge is driven from a
constant current source, the LM334, which
has a very well known and repeatable
temperature coefficient of +3300 ppm/°C.
This temperature coefficient (TC), in
conjunction with the TC of the bridge resis-
tance, is too high to compensate the
sensitivity TC, hence resistor
to reduce the total circuit TC.
R2
is
added
The basic design steps for this method
of temperature compensation are shown
below. However, please refer to SenSym’s
Application Note SSAN-16 for details on the
temperature compensation technique.
Figure IV. Constant current span TC
Compensation
a) VB = α (VS + IO R2)
( ) ( ) ( )[ ( )]b)
VB
VB
=
R•B
RB
(1 - α)+
•IO
IO
1-α
VS
VB
c) α
=
RB
R2 + RB
( ) ( )• •
d) IO = 3360 ppm/°C, RB =+750ppm/°C
IO RB
e)
IO =
67.7 mV
R1
The design steps are straight forward:
1) Knowing VS and the desired bridge
voltage VB, solve equation (b) for α.
2) Now, solve equation (c) for R2,
letting RB = 4650.
3) Solve equation (a) for IO.
4) Find R1 or its nearest 1% tolerance
value from equation (e).
Table II gives specific 1% resistor values in
ohms, for several popular system voltages.
For best results, the resistors should be 1%
metal film with a low temperature coefficient.
Table II. Selected R values vs V S for
figure IV
VS VB
5V 3V
6V 4V
9V 6V
12V 9V
15V 10V
R1()
147
105
68.1
43.2
41.2
R2()
11.0k
9.53k
9.53k
8.25k
9.53k
Amplifier design
There are hundreds of instrumentation
amplifier designs, and the intent here will
be to briefly describe one circuit which:
does not load the bridge
involves minimal components
provides excellent performance
Amplifier adjustment procedure
1. Without pressure applied,
(a) Short points A and B together as
shown in Figure V. Adjust the 1 k
common-mode rejection ( C M R R )
pot until the voltage at test point (Tp)
Vx is equal to the voltage at test
point (Tp) VR.
This is easily accomplished by
placing a digital voltmeter between
these test points and adjusting for
0.000.
March 2004 / 052
http://www.sensortechnics.com

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