SCX01DN Datasheet, PDF (8/10 Pages) List of Unclassifed Manufacturers – Precision Compensated Pressure Sensors

SCX Series
Precision compensated pressure sensors
Figure E. Timing diagram
PRESSURE SWITCH
PORTABLE PRESSURE METER
The circuit shown in Figure F is an example of using the SCX01D
to make an accurate 0.5 psi switch. This design can be easily
adapted to other pressure ranges by using higher pressure range
SCX sensors.
Circuit description
Operating the SCX01D from 5V the sensor will have ⁵/₁₂ the
sensitivity given on the SCX data sheet. The output at 0.5 psi will
be 3.75 mV. Resistor R₄ sets the amplifier gain to 269 V/V. Zener
D₁ biases the amplifier output voltage to 1.2 V with zero input
pressure and amplifier A₂ swings from 1.2 V to 3.2 V for an input
pressure from 0 to 1 psi. Resistors R₇ and R₈ provide 5 mV of
hysteresis to comparator A₃ to ensure clean transitions for slow
movins input signals. R₁₁ sets the switch point for the comparator.
Care must be taken when laying out the comparator circuit; lead
lengths should be as short as possible.
The circuit shown in Figure G is a 0 to 200 millibar portable pressure
meter. The 3 ¹/₂ digit display will read 199.9 millibar full-scale. This
circuit operates from a single 9 V battery and draws approximately
4.5 mA supply current. This will provide a typical battery life in excess
of 100 hours. The minimum battery voltage is approximately 6.5 V.
This meter provides resolution to 0.1 millibars. The same circuit
can also be used for other pressure ranges simply by changing the
sensor and gain.
Circuit description
The LM10CN (A₁) is used to generate a regulated 5 V supply to
power the SCX05DN, amplifier A₂, and the ICL7106 Amplifier A₂ is
a high input impedance diff-in,
diff-out amplifier. The sensor output is amplified to 200 mV full-
scale for the A/D input. R₅ sets the gain to 14V/V for the values
shown. The gain equation is:
Adjustment procedure
Apply 0.5 psi and adjust R₁₁ until the output just switches from a
high state (4.3 V) to a low state (0.0 V).
A_V = 2 (1 + ^R1/_R5)
R₄ is the zero adjust pot and R₈ provides the full-scale span
adjustment. The voltage from pin 35 to pin 36 is approximately 100
mV when the display reads 199.9 millibar.
Component selection
The value of the components R₆-R₁₀ and C₁-C₅ have been optimized
for 200 mV full-scale (see the Intersil ICL7106 datasheet). R₄ and
R₈ should be 15 turn cermet pots, R₆-R₁₀ are metal film 1% resistors.
C₃ the integrating capacitor should be polypropylene, the reference
and auto zero capacitors can be polystrene or mylar, the clock
capacitor, C₄, is mica.
Adjustment procedure
Apply 195 millibar to the meter and adjust R₈ until the display reads
195.0. Apply 0 psig and adjust R₄ until the display reads 000.0.
Repeat if required.
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August 2005 / 053
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