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SX15AD2 Schematic ( PDF Datasheet ) - Sensym

Teilenummer SX15AD2
Beschreibung Pressure Sensor
Hersteller Sensym
Logo Sensym Logo 




Gesamt 10 Seiten
SX15AD2 Datasheet, Funktion
SX - Series
PRESSURE SENSORS
FEATURES
www.datasheet4u.com
· 0 ... 1 to 0 ... 300 psi
· Absolute, Differential
and Gage Devices
· High Impedance Bridge
· Low Power Consumption
for Battery Operation
APPLICATIONS
· Industrial Controls
· Pneumatic Controls
· Medical Instrumentation
· Barometry
EQUIVALENT CIRCUIT
GENERAL DESCRIPTION
The SX Series of pressure sensors
provide the most cost effective method of
measuring pressures up to 150 psi. These
sensors were specifically 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 internal
vacuum reference and an output voltage
proportional to absolute pressure. The Dif-
ferential (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 psi only.
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 applications where the sen-
sing element is to be integral to the OEM
equipment. These packages can be O-ring
sealed, epoxied, and/or clamped onto a
pressure fitting. A closed bridge four-pin
SIP configuration is provided for electrical
Scale:
5mm
½ inch
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 portable and low
power or battery operated systems. Due
to its low noise, the SX is an excellent choice
for medical and low pressure
measurements.
For further technical information please
contact the factory.
ELECTRICAL CONNECTION
Button Sensor or "N" Package
Button Sensor
Buttom view (open bridge)
TO Can or DIP Package
SXxxxGD2 DIP
SXxxxAD2
SXxxxD4 DIP
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)
March 1998/052
Aubinger Weg 27, 82178 Puchheim, Germany
Phone 0049 - (0) 89 80 08 30, Fax 0049 - (0) 89 8 00 83 33
http://www.sensortechnics.com






SX15AD2 Datasheet, Funktion
SX - Series
PRESSURE SENSORS
APPLICATION INFORMATION (cont.)
w
w
wa) .VBd=VaS-4t φ a s
h
e
e
t
4
u
.
c a)oVBm= VS - α φ
( )b) VB
( ) ( )VB
=
φ
φ
VS -4
φ
( )φ
c ) φ = -2500 ppm/°C for silicon diodes
Figure II. Equations
( ) ( ) ( )
VB
b) VB
=-
φα
φ
x
VS
φ -α
c) α
=
1
+
R1
R2
( )d) φ
φ
= -2500 ppm/°C
For example, solving equation (b) for VB/
VB when
VS = 6.0 V
φ = 0.7 V
Yields:
V• B = 2188 ppm/°C
VB
Since the sensor’s span changes with
temperature 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 VS above 6V, it is
recommended 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
compensation 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.
Table I. Selected R Values vs VS for
Figure III
VS R1 () R2 ()
5V 3.32k 1.43k
9V 4.02k
806
12V 4.22k
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 compensations
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 R2 is added
to reduce the total circuit TC.
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.
a) VB = α (VS + IOR2)
( ) ( ) ( )[ ( )]• •
b) VB = RB (1 - α)+ IO 1-α VS
VB RB
IO 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 VS 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
Figure III. Transistor/Resistor
Span TC Compensation
Figure IV. Constant Current Span TC
Compensation
Amplifier Adjustment Procedure
1. Without pressure applied,
(a) Short points A and B together as
shown in Figure V. Adjust the 1k
common-mode rejection (CMRR)
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 1998/052
Aubinger Weg 27, 82178 Puchheim, Germany
Phone 0049 - (0) 89 80 08 30, Fax 0049 - (0) 89 8 00 83 33
http://www.sensortechnics.com

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