SCX - Series Precision Compensated Pressure Sensors FEATURES · 0 - 1 psi to 0 - 150 psi · Precision Temperature Compensation · Calibrated Zero and Span · Small Size · Low Noise · High Accuracy · High Impedance for Low Power Applications APPLICATIONS · Medical Equipment · Barometry · Computer Peripherals · Pneumatic Control · HVAC GENERAL DESCRIPTION The SCX series sensors will provide a very cost effective solution for pressure applications that require high accuracy over a wide temperature range. These internally calibrated and temperature compensated sensors were specifically designed to provide an accurate and stable output over a 0°C to 70°C temperature range. This series is intended for use with non-corrosive, nonionic working fluids such as air, dry gases, and the like. Devices are available to measure absolute, differential, and gage pressures from 1psi (SCX01) up to 150psi (SCX150). The Absolute (A) devices have an internal vacuum reference and an output voltage proportional to absolute pressure. The Differential (D) devices allow application of pressure to either side of the pressure sensing diaphragm and can be used for gage or differential pressure measurements. The SCX devices feature an integrated circuit sensor element and laser trimmed thick film ceramic housed in a compact nylon case. This package provides excellent corrosion resistance and provides isolation to external package stresses. The package has convenient mounting holes and pressure ports for ease of use with standard plastic tubing for pressure connection. All SCX devices are calibrated for span to within ±1% and provide a very low zero pressure output of ±300 microvolts maximum. Thus, for many applications,no trimming networks are required in the signal conditioning circuitry. If the application requires extended temperature range ope- Scale: 1cm ½ inch ration, beyond 0 to 70°C, two pins which provide an output voltage proportional to temperature are available for use with external circuitry. The output of the bridge is ratiometric to the supply voltage and operation from any D.C. supply voltage up to +30 V is acceptable. Because these devices have very low noise and excellent temperature compensation, they are ideal for medical and other high performance applications. The 100 microsecond response time also makes this series an excellent choice for computer peripherals and pneumatic control applications. EQUIVALENT CIRCUIT ELECTRICAL CONNECTION Pin 1) Pin 2) Pin 3) Pin 4) Pin 5) Pin 6) Temperature Output (+) VS Output (+) Ground Output (-) Temperature Output (-) Note: The polarity indicated is for pressure applied to port B. (For absolute devices pressure is applied to port A and the output polarity is reversed.) March 1998/053 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 SCX - Series Precision Compensated Pressure Sensors PRESSURE SENSOR CHARACTERISTICS1 STANDARD PRESSURE RANGES PART NUMBER OPERATING PRESSURE SCX01DN 0 - 1 psid SCX05DN 0 - 5 psid SCX15AN 0 - 15 psia SCX15DN 0 - 15 psid SCX30AN 0 - 30 psia SCX30DN 0 - 30 psid SCX100AN 0 - 100 psia SCX100DN 0 - 100 psid SCX150AN 0 - 150 psia 0 - 150 psid SCX150DN * Maximum pressure above which causes permanent sensor failure Maximum Ratings (For All Devices) Supply Voltage VS Common-mode Pressure Lead Temperature (Soldering, 4 seconds) FULL-SCALE SPAN2 PROOF PRESSURE* 20 psid 20 psid 30 psia 30 psid 60 psia 60 psid 150 psia 150 psid 150 psia 150 psid Min. 17.82 mV 59.4 mV 89.1 mV 89.1 mV 89.1 mV 89.1 mV 99.0 mV 99.0 mV 89.1 mV 89.1 mV Typ. 18 mV 60 mV 90 mV 90 mV 90 mV 90 mV 100 mV 100 mV 90 mV 90 mV Environmental Specifications +30 VDC 50 psig 250°C Max. 18.18 mV 60.6 mV 90.9 mV 90.9 mV 90.9 mV 90.9 mV 101.0 mV 101.0 mV 90.9 mV 90.9 mV (For All Devices) Temperature Range Compensated Operating Storage Humidity Limits 0 to 70°C -40°C to +85°C -55°C to +125°C 0 to 100 %RH COMMON PERFORMANCE CHARACTERISTICS1 Characteristic Zero Pressure Offset Combined Linearity and Hysteresis3 Temperature Effect on Span (0-70°C)4 Temperature Effect on Offset (0-70°C)4 Repeatability5 Input Impedance 6 Output Impedance7 Common-mode Voltage8 Response Time 9 Long Term Stability of Offset and Span10 Min. Typ. Max. Unit -300 ------------5.8 ----- 0 ±0.1 ±0.2 ±100 ±0.2 4.0 4.0 6.0 100 ±0.1 +300 ±0.5 ±1.0 ±500 ±0.5 ----6.2 ----- µV %FSO %FSO µV %FSO kΩ kΩ VDC µsec %FSO SPECIFICATION NOTES: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Reference conditions: Unless otherwise noted: Supply voltage, VS = 12 V, TA = 25°C, Common-mode Line Pressure = 0 psig, Pressure Applied to Port B. For absolute devices only, pressure is applied to Port A and the output polarity is reversed. Span is the algebraic difference between the output voltage at full-scale pressure and the output at zero pressure. Span is ratiometric to the supply voltage. See Definition to Terms. Hysteresis - the maximum output difference at any point within the operating pressure range for increasing and decreasing pressure. Maximum error band of the offset voltage and the error band of the span, relative to the 25°C reading. Maximum difference in output at any pressure with the operating pressure range and temperature within 0°C to +50°C after: a) 1,000 temperature cycles, 0°C to +70°C b) 1.5 million pressure cycles, 0 psi to full-scale span Input impedance is the impedance between pins 2 and 4. Output impedance is the impedance between pins 3 and 5. This is the common-mode voltage of the output arms (Pins 3 and 5) for VS = 12 VDC. Response time for a 0 psi to full-scale span pressure step change, 10% to 90% rise time. Long term stability over a one year period. Maximum zero pressure offset for absolute devices is 0 ±500 µV. March 1998/053 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 SCX - Series Precision Compensated Pressure Sensors TYPICAL PERFORMANCE CHARACTERISTICS GENERAL DISCUSSION The SCX series devices give a voltage output which is directly proportional to applied pressure. The devices will give an increasing positiv going output when increasing pressure is applied to pressure port PB of the device. If the input pressure connections are reversed, the output will increase with decreases in pressure. The devices are ratiometric to the supply voltage and changes in the supply voltage will cause proportional changes in the offset voltage and full-scale span. Since for absolute devices pressure is applied to port PA, output polarity will be reversed. User Calibration The SCX devices are fully calibrated for offset and span and should therefore require little if any user adjustment in most applications. For precise span and offset adjustments, refer to the applications section herein. Vacuum Reference (Absolute Device) Absolute sensors have a hermetically sealed vacuum reference chamber. The offset voltage on these units is therefore measured at vacuum, 0 psia. Since all pressure is measured relative to a vacuum reference,all changes in barometric pressure or changes in altitude will cause changes in the device output. Media Compatibility SCX devices are compatible with most non-corrosive gases. Because the circuit is coated with a protective silicon gel, many otherwise corrosive environments can be compatible with the sensors. As shown in the physi-cal construction diagram below, fluids must generally be compatible with silicon gel, plastic, aluminium, RTV, silicon, and glass for use with Port B. For questions concerning media compatibility, contact the factory. MECHANICAL AND CONSIDERATIONS MOUNTING The SCX nylon housing is designed for convenient pressure connection and easy PC board mounting. To mount the device horizontally to a PC Board, the leads can be bent downward and the package attached to the board using either tie wraps or mounting screws. For pressure attachment, tygon or silicon tubing is recommended. All versions of the SCX sensors have two (2) tubes available for pressure connection. For absolute devices, only port PA is active. Applying pressure through the other port will result in pressure dead ending into the backside of the silicon sensor and the device will not give an output signal with pressure. For gage applications, pressure should be applied the port PB . Port PA is then the vent port which is left open to the atmosphere. For differential pressure applications, to get proper output signal polarity, port PB should be used as the high pressure port and PA should be used as the low pressure port. March 1998/053 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 SCX - Series Precision Compensated Pressure Sensors Physical Construction (Cutaway Diagram) (Not drawn to scale) APPLICATION INFORMATION The following circuits show some typical designs using the SCX series sensors. For specific applications information or assistance, please contact your nearest Sensym sales office or the Sensym factory. Adjustment Procedure 1. With zero-pressure applied, adjust the offset adjust R 3, until VOUT = 2.000 V 2. Apply full-scale pressure (10 in. W.C) to port B1 and adjust the full-scale adjust R2, so that V OUT = 5.000 V. Low Pressure Applications For sensing pressures below 1 psi, the circuit shown in Figure A uses the SCX01DN to provide a 2 to 5 V output for a 0 to 10 inch of water column input pressure. This output signal is compatible with many A/D converters and hence can be used to interface to a microprocessor system. This low-cost circuit is easily adaptable to lower full-scale pressures down to 5 inches of water column. Circuit Description The LM10 is used to provide a voltage reference for the excitation voltage (VE), and for the voltage node VREF. With this configuration, VE and VREF are not affected by noise or voltage variations in the 12 V power supply. R3 is used to adjust VREF to set the initial offset voltage at the output, VOUT. The pressure signal, VIN, is amplified by amplifiers B1, and B2. (See Sensym Application Note SSAN-17A for details on this amplifier) R2 is used to adjust the signal gain of the circuit. The output equation is given below. VOUT = VIN [ 2 (1+ R/R1)]+VREF For the best circuit performance, a careful selection of components in necessary. Use wirebound pots of insure low temperature coefficients and low longterm drift. A five-element resistor array (10kΩ) SIP should be used for the resistors in the amplifier stage in order to obtain closely matched values and temperature coefficients. All other resistors should be 1% metal film. Amplifiers B1 , and B2 should have low offset voltage and low noise. Signal lines should be as short as possible and the power supply should be capacitively bypassed on the PC board. 3. Repeat procedure if necessary. Medical Applications For blood pressure monitoring applications, the circuit shown in Figure B provides a 0.5 V to 3.5 V output for a 0 to 300 mm Hg input pressure. The circuit is easily calibrated and is not affected by changes in the voltage supply. Because 300 mm Hg is approximately 5.8 psi, an SCX05DN is used. Circuit Description The circuit shown here in Figure B is very similar to that shown in Figure A. The internal 200 mV reference voltage of the LM10 is amplified to provide power to the sensor and to provide a voltage reference, VREF . This allows the circuit to operate at a supply voltage between 5 and 20 volts without affecting performance of the circuit. By adjusting R3 , VREF is used to set the initial zeropressure voltage at VOUT. The pressure signal, VIN , is amplified by amplifiers B1 and B2. These amplifiers should be precision op amps with low offset voltages and high common-mode rejection. The signal gain is adjusted by R2 , and the overall equation for the output voltage is given by , VOUT = VIN [ 2 (1+ R/R1)]+VREF Adjustment Procedure 1. With zero-pressure applied, adjust the offset adjust R3, until VOUT = 0.500 V 2. Apply full-scale pressure (300 mm Hg) to port B1 and adjust R2, until VOUT = 3.500 V. 3. Repeat procedure if necessary. March 1998/053 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 SCX - Series Precision Compensated Pressure Sensors APPLICATION INFORMATION (cont.) Parallel A/D Conversion Serial A/D Conversion The SCX sensor can be easily interfaced to a microprocessor bus. Using an A/D converter, for a 0 to 1 psig input, the circuit in Figure C will provide an eight-bit parallel output which is proportional to applied pressure. The circuit allows for easy calibration and uses a single 5V supply. The circuit shown in Figure D is similar to that shown in Figure C, except the output is bit serial. Also shown (under the dashed line) is a complimentary circuit for converting the serial output to a parallel output for simplified testing. Circuit Description Circuit Description The output signal of the sensor is amplified by A1, and A 2. The pot, in resistor R 1, can be adjusted to calibrate the gain of the circuit as shown in the following gain equation: VOUT = VIN 2 [1+ R/R1] VOUT = V IN By adjusting R3 , VIN (-) on the A/D converter is used to adjust the initial offset voltage. A zener diode (LT1004) sets the initial input voltage and provides the reference voltage for the converter. The converter will output the maximum digital code when the A/D converter´s input voltage, V OUT, is twice the zener voltage, minus 1 1/ 2 LSB. The A/D converter, as shown, is a free-running configuration where the binary output is updated continously*. The only requirement is that the WR and INTR must be momentarily grounded after power-up to ensure proper operation. Adjustment Procedure 1. With no pressure applied, adjust the offset pot R3 until all bits are zero except the LSB, which should be switching between one and zero. 2. Apply full-scale pressure (1 psig) to port B, and adjust the fullscale pot R2 until all bits are ones except the LSB which should be flickering between one and zero. 3. Repeat procedure if necessary. The three op amp configuration allows VOUT to be at the same common-mode voltage as VIN , and takes advantage of the excellent CMRR of the ADC0831. R2 is used to adjust the gain of the amplifier such that 2 [3 /2+ 2R/R1] The A/D converter will output the maximum digital code when VOUT is equal to the zener voltage minus 1 1/2 LSB. the initial offset of the circuit can be nulled out by adjusting pot R3. The converter circuit requires only a clock and a chip select (CS) line in order to operate. As shown in Figure E, when CS goes low, the A/D converter will start a new conversion on the next rising edge of the clock. On the next falling edge of the clock, DO will have a zero start bit. Then, starting with the MSB, the data out line (DO ) will provide the converted digital output during the next eight consecutive falling edges of the clock. The serial output can be read by using an oscilloscope, a microprocessor, or a simple serial-to-parallel converter as shown in Figure D. Adjustment Procedure 1. With zero-pressure, adjust R3, until the output of the A/D converter is alternating between 00 and 01 (HEX). 2. Apply full-scale pressure (1 psig) to port B, and adjust R4 unti l the digital output alternates between the FE to FF transition. 3. Repeat procedure if necessary. * For timing specifications and bus interface, see the ADC0804 Datasheet from National Semiconductor. Figure A. Low Pressure Circuits Provide a 2 to 5 V Output for a 0-10 in. W.C. Pressure Input March 1998/053 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 SCX - Series Precision Compensated Pressure Sensors Figure B. Medical Application Circuit Provide a 0.5 to 3.5 V Output for a 0-300mmHg Pressure Input Figure C. A Parallel A/D Conversion Circuit for 0-1 psig Applications. March 1998/053 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 SCX - Series Precision Compensated Pressure Sensors Figure D. Serial A/D Conversion for 0-1 psig Applications and Simple Test Circuit Figure E. Timing Diagram March 1998/053 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 SCX - Series Precision Compensated Pressure Sensors PRESSURE SWITCH 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. 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 Circuit Description 5 Operating the SCX01D from 5V the sensor will have /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. 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). PORTABLE PRESSURE METER 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. Figure F. 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 fullscale for the A/D input. R5 sets the gain to 14V/V for the values shown. The gain equation is: AV = 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. 0.5 psi Switch March 1998/053 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 SCX - Series Precision Compensated Pressure Sensors Figure G. 0-200 millibar meter. PHYSICAL DIMENSIONS March 1998/053 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 SCX - Series Precision Compensated Pressure Sensors ORDERING INFORMATION To order, use the following part number(s). Description Part Number 0 to 1 psi Differential/Gage SCX01DN 0 to 5 psi Differential/Gage SCX05DN 0 to 15 psi Absolute SCX15AN 0 to 15 psi Differential/Gage SCX15DN 0 to 30 psi Absolute SCX30AN 0 to 30 psi Differential/Gage SCX30DN 0 to 100 psi Absolute SCX100AN 0 to 100 psi Differential/Gage SCX100DN 0 to 150 psi Absolute SCX150AN 0 to 150 psi Differential/Gage SCX150DN Mounting Accessories Description Xmas Tree Clip Part Number SCXCLIP 6 Pin Rigth Angle Socket SCXCNCT Pressure Tubing Clamp SCXSNP1 SenSym and Sensortechnics reserve the right to make changes to any products herein. SenSym and Sensortechnics do not assume any liability arising out of the application or use of any product or circuit described herein, neither does it convey any license under its patent rights nor the rights of others. March 1998/053 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