datasheet sx01dn.pdf

8/2/2019 datasheet sx01dn.pdf

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SX SeriesPressure sensors

1/10July 2008 / 052

www.sensortechnics.com

SXxxxGD2 DIP SXxxxAD2

SXxxxD4 DIP

Button sensor or "N" package

Output

Vs

+

-

Vs

-

Output

+

FEATURES

0...1 to 0...150 psi

Absolute, differentialand gage devices

High impedance bridge

Low power consumptionfor battery operation

APPLICATIONS

Industrial controls

Pneumatic controls

Medical instrumentation

Barometry

GENERAL DESCRIPTION

The SX series of pressure sensorsprovides the most cost effectivemethod of measuring pressures upto 150 psi. These sensors werespecifically designed to be used withnon-corrosive and non-ionic media,such as air and dry gases. Convenientpressure ranges are available tomeasure differential, gage andabsolute pressures from 0 to 1 psi upto 0 to 150 psi.

The absolute (A) devices have an in-ternal vacuum reference and an outputvoltage proportional to absolutepressure. The differential (D) devicesallow application of pressure to eitherside of the diaphragm and can beused for gage or differential pressuremeasurements.

This product is packaged either inSenSym's standard low cost chipcarrier "button" package, a plasticported "N" package or a dual inlinepackage (DIP). All packages aredesigned for applications where thesensing element is to be integral tothe OEM equipment. These packages

can be o-ring sealed, epoxied, and/orclamped onto a pressure fitting.A closed bridge 4-pin SIP configurationis provided for electrical connection tothe button or "N" package.

Because of its high-impedancebridge, the SX series is ideal forportable and low power or batteryopera-ted systems. Due to its lownoise, the SX is an excellent choicefor medical and low pressuremeasurements.

The polarity indicated is for pressure applied to:SX... : P1 (forward gage)SX...AD2 : P1 (forward gage)SX...GD2 : P2 (backward gage)SX...DD4 : P2 (backward gage)

ELECTRICAL CONNECTION

Button sensor

+VS 3

out - 4

1GND

out + 2P1

DIP package

EQUIVALENT CIRCUIT

P1GND

+Vs 4

vent hole

out - 4out + +Vs out -

+Vs 1P2 out +

GND

1 P1out -

GND

+Vs 1out +

4 +VsP2

+Vs


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Maximum ratings

Suppy voltage, VS

+12 VDC

Temperature rangesOperating -40C to +85CStorage -55C to +125C

Maximum pressure at any port11 150 psig

Lead temperature (soldering 4 sec.) 250 C

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tesffoerusserporeZ 9 53- 02- 0 Vm

stceffeerutarepmeT tesffO 4 C/V/V

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siseretsyhdnaytiraenildenibmoC 2 2.0 5.0SSF%

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3

5.0napsdnatesffofoytilibatsmretgnoL 6 1.0 Vm

ecnadepmitupnI 1.4k

ecnadepmituptuO 1.4

emitesnopseR 5 1.0 sm

PERFORMANCE CHARACTERISTICS(V

s= 5.0 0.01 V, t

amb= 25 C, common-mode pressure = 0 psig, pressure applied to P1 for Button, N and A2

housings, pressure applied to P2 for G2 and D4 housings)

PRESSURE SENSOR CHARACTERISTICS

(Vs = 5.0 0.01 V, tamb = 25 C, common-mode pressure = 0 psig, pressure applied to P1 for Button, N and A2housings, pressure applied to P2 for G2 and D4 housings)

rebmuntraP erusserpgnitarepO erusserpfoorP 8napselacs-lluF 1

.niM .pyT .xaM

...10XS isp1...0 isp02 Vm51 Vm02 Vm52

...50XS isp5...0 isp02 Vm05 Vm57 Vm001

...51XS isp51...0 isp03 Vm57 Vm011 Vm051

...03XS isp03...0 isp06 Vm57 Vm011 Vm051

...001XS isp001...0 isp051 Vm001 Vm051 Vm002

...051XS isp051...0 isp002 Vm57 Vm011 Vm051


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TYPICAL PERFORMANCE CHARACTERISTICS

Specification notes:

1.2.

3.

4.

5.6.7.8.

9.

Span is the algebraic difference between the output voltage at full-scale pressure and the output at zero pressure.Hysteresis is the maximum output difference at any point within the operating pressure range for increasing and decreasing

pressure. Linearity is the maximum deviation of measure output at constant temperature (25C) from "Best Straight Line"determined by three points, offset, full scale pressure and half full scale pressure.Maximum difference in output at any pressure with the operating pressure range and temperature within 0C to +70C after:a) 100 temperature cycles, 0C to +70Cb) 1.0 million pressure cycles, 0 psi to full scale spanSlope of the best straight line from 0C and 70C. For operation outside this temperature, contact Sensortechnics for morespecific applications information.Response time for a 0 to full-scale span pressure step change.Long term stability over a one year period .This parameter is not 100 % tested. It is guaranteed by process design and tested on a sample basis only.If the proof pressure is exceeded, even momentarily, the package may leak or burst, or the pressure sensing die may fracture.Note: The proof pressure for the forward gage of all devices in the D4-package is the specified value or 100 psi, whatever is less.The zero pressure offset is 0 mV Min, 20 mV Typ and 35 mV Max for part nos. SX...G2 and SX...D4.


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MECHANICAL AND MOUNTING CONSIDERATIONS

PHYSICAL CONSTRUCTION

Button sensor elementThe button sensor element was designedto allow easy interface with additionalcases and housings which then allowpressure connection. The device can bemounted with an o-ring, gasket, or RTVseals on one or both sides of the device.The device can then be glued or clampedinto a variety of fixtures and the leads canbe bent as necessary to allow for ease ofelectrical connection. However, caution isadvised as repeated bending of the leadswill cause eventual breakage.

For most gage applications, pressureshould be applied to the top side of the

device (see Physical ConstructionDrawing). For differential applications, thetop side of the device (P1) should be usedas the high pressure port and the bottom(P2) as the low pressure port.

The button SX package has a very smallinternal volume of 0.06 cubic centimetersfor P1 and 0.001 cubic centimeters for P2.

N packaged sensorThe "N packaged sensor is designed forconvenient pressure connection and easyPC board mounting. To mount the devicehorizontally to a PC board, the leads can be

bent downward and the package attachedto the board using either tie wraps ormounting screws. For pressureattachment, tygon or silicon tubing isrecommended.

The N package version of the sensor hastwo (2) tubes available for pressureconnec-tion. For gage devices, pressureshould be applied to port P1. For differentialpressure applications, port P1 should beused as the high pressure port and P2should be used as the low pressure port.

GENERAL DISCUSSION

Output characteristicsThe SX series devices give a voltage outputwhich is directly proportional to appliedpressure. The devices will give an increasein positive going output when increasingpressure is applied to pressure port P1 ofthe device. If the devices are operated inthe backward gage mode, the output willincrease with decreases in pressure. Thedevices are ratiometric to the supplyvoltage. Changes in supply voltage willcause proportional changes in the offsetvoltage and full-scale span.

User calibrationSX series devices feature the button ICpressure sensor element. This will keepoverall system costs down by allowingtheuser to select calibration and temperaturecompensation circuits which specificallymatch individual application needs. In most

cases, the primary signal conditioningelements to be added to the SX by the userare: offset and span calibration andtemperature compensation.

Some typical circuits are shown in theapplication section.

Vacuum reference (absolutedevices)Absolute sensors have a hermeticallysealed vacuum reference chamber. Theoffset voltage on these units is thereforemeasured at vacuum, 0 psia. Since allpressure is measured relative to a vacuumreference, all changes in barometricpressure or changes in altitude will causechanges in the device output.

Media compatibilitySX devices are compatible with most non-corrosive gases. Because the circuitry iscoated with a protective silicon gel, some

otherwise corrosive environments can becompatible with the sensors. As shown inthe physical construction diagram belowfor the button sensor element and ,,Npackage, fluids must generally becompatible with silicon gel, RTV, plastic, andaluminum for forward gage use and RTV,silicon, glass and aluminum for backwardgage or differential applications. Forquestions concerning media compatibility,contact the factory.


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GeneralThe SX family of pressure sensors functionsas a Wheatstone bridge. When pressure isapplied to the device (see Figure I) theresistors in the arms of the bridge changeby an amount .

Figure I. Button sensor bridgeschematic

The resulting differential output voltage V0is easily shown to be VO= VB x . Sincethe change in resistance is directly pro-portional to pressure, VO can be written as:

VO = S x P x VB VOS (1)

Where: VO is the output voltage in mVS is the sensitivity in mV/V per psiP is the pressure in psiV

Bis the bridge voltage in volts.

VOS is the offset error (the differential outputvoltage when the applied pressure is zero).The offset voltage presents little problem inmost applications, since it can easily becorrected for in the amplifier circuitry, orcorrected digitally if a microprocessor isused in the system.

Temperature effectsIn this discussion, for simplicity of notation,the change of a variable with temperaturewill be designated with a dot () over thevariable. For example,

change in sensitivity Schange in temperature T

From equation (1), and ignoring the VOSterm, it in seen that for a given constantpressure, the output voltage change, as afunction of temperature*, is:

VO = SPVB (2)

Thus, in order for output voltage to be inde-pendent of temperature, the voltage acrossthe bridge, VB, must change with tempera-ture in the "opposite direction from thesensitivity change with temperature. Fromthe typical curves for the temperaturedependence of span (span = S x P x VB),

APPLICATION INFORMATION

S = =

it can be seen that the sensitivity changewith temperature is slightly non-linear andcan be correlated very well with an equationof the form:

S = SO[(1 - TD) + TD2] (3)

where TD is the temperature differencebetween 25C and the temperature of inte-rest, SO is the sensitivi ty at 25C, and beta() and rho () are correlation constants.Fortunately, between 0C and 70C thechange in sensitivity with temperature isquite linear, and excellent results can beobtained over this temperature range byignoring the second-order temperaturedependent term. Operating outside the 0C

and 70C temperature range will require amore rigorous mathematical approach andthe use of non-linear compensating cir-cuitry, if accuracy of better than 1 % is re-quired. Because the majority of SX appli-cations fall within the 0C to 70C operatingtemperature range, the discussion andcircuit designs given here will ignore thenon-linear effects.Thus:

S = SO (1 - TD) (4)

Substituting equation (4) into equation (1)and ignoring VOS, it can be shown that thenecessary bridge voltage, VB, will be of the

form:VBO(1-TD)

where VBO is the bridge voltage at 25C.This equation is again non-linear.

However, for the temperature range ofinterest, and since is small (0.215%/Cfrom the electrical tables), the aboveexpression can be approximated by:

VB=VBO [1 +TD]

with less than 1 % error. Thus to compen-sate for a negative 2150 ppm/C sensitivitychange with temperature, the bridge voltageshould increase with temperature at a rate

of +2150 ppm/C.The above value of bridge voltage changewill be used in the circuit discussions thatfollow. That is to say, the required changein terms of ppm/C is:

= +2050 ppm/C

The bridge input resistance*, RB alsochanges with temperature and is quite linearin the temperature range of interest. Thebridge resistance has a temperaturecoefficient of typically:

= +750 ppm/C

VB = =VBO [(1 - TD + (TD)2+...)]

This term enters into several compensationcircuit equations, particularly when thebridge excitation is from a constant currentsource.

To summarize, the following list indicateshow the sensor variables can be accommo-dated Full-scale span from device to device.

Make the gain adjustment in the op ampcircuitry

Temperature coefficient of span:1) temperature compensate the bridge or2) temperature compensate the op amp

gain Offset voltage:

Adjustment in op amp circuitry Offset voltage temperature coefficient:Usually can be ignored. For more precisedesign requirements, contact the factoryfor information on how to compensate forthis term.

Bridge compensation circuitsAlthough thermistors can be used to tempe-rature compensate the bridge (and in factwill be required for extended temperatureoperation), they are inherently non-linear,difficult to use in volume production, andmore expensive than the circuit approachesshown here, which use inexpensive semi-conductor devices The circuits shown havebeen designed to incorporate a minimumnumber of adjustments and allow inter-changeability of devices with little variationfrom device to device. In general, equationsfor the bridge voltage and its change withtemperature are given to enable the user tomodify or adjust the circuitry as required.

1. Diode string (Figure II)For systems using 6 V supplies, this methodof compensating for the effects of span overtemperature is the lowest cost solution Thediodes are small signal silicon diodes, suchas 1N914 or 1N4148, and do not have tobe matched.

Figure II. Diode String SpanCompensation

VBVB( )

RBR

B

( )


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( )[ ( )]

IO RBIO RB

( )

a) VB = (VS + IOR2)

b) = (1 - )+ 1-

c) =

d) = 3360 ppm/C, =+750ppm/C

e) IO =

The design steps are straight forward:

1) Knowing VS and the desired bridgevoltage VB, solve equation (b) for .

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 inohms, 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 IVVS VB R1() R2()

5V 3V 147 11.0k

6V 4V 105 9.53k

9V 6V 68.1 9.53k

12V 9V 43.2 8.25k

15V 10V 41.2 9.53k

Amplifier designThere are hundreds of instrumentationamplifier designs, and the intent here willbe to briefly describe one circuit which: does not load the bridge involves minimal components

provides excellent performance

Amplifier adjustment procedure1. Without pressure applied,

(a) Short points A and B together asshown in Figure V. Adjust the 1 kcommon-mode rejection ( C M R R )pot until the voltage at test point (Tp)Vx is equal to the voltage at testpoint (Tp) VR.

This is easily accomplished byplacing a digital voltmeter betweenthese test points and adjusting for0.000.

VB RB IO VSVB RB IO VB( ) ( )

67.7 mVR1

RBR2 + RB

( )

a) VB=VS-4

b) VBVB VS

c) = -2500 ppm/C for sil icon diodes

Figure II. Equations

For example, solving equation (b) for VB/VB when

VS = 6.0 V

= 0.7 V

Yields:

= 2188 ppm/C

Since the sensors span changes with tem-perature at -2150 ppm/C, this technique willtypically result in an overall negative TC of38 ppm/C. This error is acceptable in mostapplications.

For operation with VS above 6V, it is recom-mended to use the transistor or constantcurrent compensation technique.

2. Transistor compensation networkFigure III uses a single transistor to simulatea diode string, with the equations as shown.The values shown in Table I were found togive excel lent results over 0C to 70C.Again, if precision temperature compen-sation is required for each device, the fixedvalue resistors shown for R1 in Table I canbe replaced by a 3.24k resistor in series witha 1k pot. Then, each devices temperaturecompensation can be individually adjusted.

Figure III. Transistor/Resistorspan TC compensation

-4

( )( )

( )

( )

=

VBVB

a) VB= VS -

b) = - x-

c) = 1 +

d)

Table I. Selected R values vs VS forfigure III

VS R1 () R2 ()

5V 3.32k 1.43k

9V 4.02k 80612V 4.22k 604

3. Constant current excitation(Figure IV)The circuits shown in Figures II and III,although simple and inexpensive, have onedrawback in that the voltage across thebridge is determined by the compensationnetwork. That is, the compensation networkis determined and what voltage is leftover"is across the bridge. The circuit of FigureIV solves this problem and allows the bridgevoltage to be independently selected. InFigure IV, the bridge is driven from a

constant current source, the LM334, whichhas a very well known and repeatabletemperature coefficient of +3300 ppm/C.This temperature coefficient (TC), inconjunction with the TC of the bridge resis-tance, is too high to compensate thesensitivity TC, hence resistor R2 is addedto reduce the total circuit TC.

The basic design steps for this methodof temperature compensation are shownbelow. However, please refer to SenSymsApplication Note SSAN-16 for details on thetemperature compensation technique.

Figure IV. Constant current span TCCompensation

( ) ( ) ( )VB VB VS

R1R2

= -2500 ppm/C( )

APPLICATION INFORMATION (cont.)


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Table III. For 0 to 70C operation

SPAN

VS VB R2 R1 FS R5 Rp5V 3.5V 9.09k 118 3V 604 2k

6V 4.5V 8.45k 86.6 4V 604 2k

9V 7V 7.87k 54.9 5V 1k 2k

12V 10V 7.15k 36.5 5V 1.82k 5k

12V 10V 7.15k 36.5 10V 511 2k

15V 12V 7.68k 31.6 5V 1.4k 5k

15V 12V 8.87k 31.6 10V 604 2k

APPLICATION INFORMATION (cont.)

(b) Remove the short and adjust the500 offset adjust pot until Vx isagain equal to VR.

(c) Adjust the 2k reference (VR) adjustpot to get an output voltage (VO)equal to 1.00V.

2. Apply the fuII-scale pressure and adjustthe span adjust pot, R5, to get the outputvoltage that is desired to represent full-scale.

Note: Application information shown here is based on the closed bridge configuration.

The choice of the operational amplifiers touse is based on individual cost/performancetrade-offs. The accuracy will be primarilylimited by the amplifiers common-moderejection, offset voltage drift with tempera-ture and noise performance. Low cost, lowperformance devices, such as the LM324can be used if the temperature rangeslimited to 25C +15C and an accuracy of+2% is adequate.

For more precise applications amplifierssuch as the LT1014 and LT1002 have beenfound to be excellent.

An amplifier that uses a single supply isshown in Figure V. Table III gives resistorvalues for various supply and full-scaleoutput combinations.

Factory compensated devicesThis application note provides the neces-sary information for temperature compen-sating and calibrating the SX sensors. Insome case, the customer may find that SXdevices which have been factory adjustedfor temperature compensation and span are

more economical for a particular application.SenSym does offer devices with this feature.For more information on these factorycalibrated and compensated devices, theSCX series and SDX series, please contactSensortechnics.

Figure V: Button Sensor Amplifier Circuit

A = LT1014CN VO

= 4 [1 + ] VIN

+ VR

B = LM10CN

Resistors labled R3

are 5-ElementResistor Arrays 10 k. Two required

10kR

G


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PHYSICAL DIMENSIONS

Button package

N package

mass: 1 g dimensions in inches (mm)



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PHYSICAL DIMENSIONS

Basic sensor DIP "D2" package

Basic sensor DIP "D4" package



0.020 typ.(0.51)

0.110 typ.(2.79)

0.380(9.65)0.285

(7.24)

0.090 typ.(2.29)

0.470(11.94)0.050

typ.(1.27)

0.550(13.97)

P2

P1

0.600(15.24)

0.01(0.25) 0.100 typ.

(2.54)

0.300(7.62)

0.070(1.78)

0.135(3.43)

0.250(6.35)


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ORDERING INFORMATION

SenSym and Sensortechnics reserve the right to make changes to any products herein. SenSym and Sensortechnics do not assume anyliability 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.

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isp51-0 A51XS NA51XS 2DA51XS ---

isp03-0 A03XS NA03XS 2DA03XS ---

isp001-0 A001XS NA001XS 2DA001XS ---

isp051-0 A051XS --- --- ---

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isp5-0 2DG50XS ---

isp51-0 2DG51XS ---

isp03-0 2DG03XS ---

isp001-0 2DG001XS ---

isp051-0 --- ---

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isp1-0 D10XS ND10XS --- 4DD10XS




isp001-0 D001XS ND001XS --- 4DD001XS

isp051-0 D051XS ND051XS --- ---

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datasheet sx01dn.pdf