SX100DN SENSYM, SX100DN Datasheet - Page 6

• Manufacturer Part Number: SX100DN
• Description: PRESSURE SENSOR, 0-100PSI
• Manufacturer: SENSYM

Specifications of SX100DN

• External Depth: 10.2mm
• External Length / Height: 27.2mm
• External Width: 29.2mm
• Fixing Centres: 22.9mm
• Hysteresis: 0.5%
• Lead Spacing: 2.54mm
• Linearity: 0.2%
• Operating Pressure Range: 0 To 100psid

SX Series
Pressure sensors
APPLICATION INFORMATION (cont.)
a) V B =V S -4φ
b) V B
c)
For example, solving equation (b) for V B /
V B when
Yields:
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.
6/10
( ) (
( )
V B
V S = 6.0 V
φ
Figure III. Transistor/Resistor
•
φ
φ
V B
V B
•
span TC compensation
= 0.7 V
= -2500 ppm/°C for silicon diodes
=
Figure II. Equations
= 2188 ppm/°C
( )
V S
φ
φ
φ
•
-4
)
a) V B = V S - α φ
b)
c) α
d) φ
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 R 2 is added
to reduce the total circuit TC.
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
( )
Table I. Selected R values vs V S for
( )
φ
The basic design steps for this method
•
12V
V S
5V
9V
V B
V B
•
=
=
1
-2500 ppm/°C
Compensation
= -
+
figure III
R 1 (Ω)
3.32k
4.02k
4.22k
R 1
R 2
( ) (
φ
φ
•
x
V S
φ
R 2 (Ω)
1.43k
α
- α
806
604
)
a)
b)
c)
d)
e)
1) Knowing V S and the desired bridge
2) Now, solve equation (c) for R 2 ,
3) Solve equation (a) for I O .
4) Find R 1 or its nearest 1% tolerance
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.
Amplifier design
There are hundreds of instrumentation
amplifier designs, and the intent here will
be to briefly describe one circuit which:
•
•
•
Amplifier adjustment procedure
1. Without pressure applied,
www.sensortechnics.com
Table II. Selected R values vs V S for
( )
(a) Short points A and B together as
12V
15V
( ) ( )
V S
5V
6V
9V
V B
V B
•
I O
I O
The design steps are straight forward:
voltage V B , solve equation (b) for α.
letting R B = 4650Ω.
value from equation (e).
V B =
α
I O =
does not load the bridge
involves minimal components
provides excellent performance
shown in Figure V. Adjust the 1 k
common-mode rejection ( C M R R )
pot until the voltage at test point (T p )
V x is equal to the voltage at test
point (T p ) V R .
This is easily accomplished by
placing a digital voltmeter between
these test points and adjusting for
0.000.
= 3360 ppm/°C,
=
=
R B
R B
•
67.7 mV
10V
V B
3V
4V
6V
9V
R 2 + R B
R 1
α (V S + I O R 2 )
(1 - α)+
figure IV
R B
( )
( )[ ( )]
R 1 (Ω)
R B
•
R B
43.2
41.2
68.1
147
105
•
I O
I O
July 2008 / 052
=+750ppm/°C
1-α
R 2 (Ω)
11.0k
9.53k
9.53k
8.25k
9.53k
V B
V S