TechnicalInformationTI 352C/24/ae

Sterilizable IsFET sensor forpH MeasurementTopHit CPS 441

Ion-selective field effect transistor with KCIreference electrode for blocking media

Application Areas• Maximum measuring accuracy• Blocking media (pressurized)• High organic solvent contents• Low conductivities• Used in hazardous areas; FM, CSA,

and ATEX approved

Features and Benefits• Resistant to breakage

– no glass, sensor body madecompletely of PEEK (FDAcompliant

– direct installation into the processreduced effort and costsfor sampling and laboratoryanalysis

• Refillable liquid KCI referenceelectrolyte

• Application possible at lowtemperatures– short response time– constant high accuracy

• Sterilizable• Longer calibration intervals than

glass electrodes– Lower hysteresis with alternating

temperatures– Low measuring error after high-

temperature loading– Almost no acid and alkaline errors

• With built-in temperature sensor foreffective temperature compensation

• Ideal for CIP processes whencombined with an automaticretractable holder assembly

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TopHit CPS 441

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Operating function and design

Ion-selective (more general, ion-sensitive) field effect transmitters (IsFET) weredeveloped in the 1970’s as an alternative to the glass electrode for pH measurement.

BasicsIon-selective field effect transistors use a MOS (Metal Oxide Semiconductor) transis-tor arrangement (first figure below) where the metallic gate is not a control electrode.Instead, the medium in the IsFET is in direct contact with the gate isolator layer(second figure below). Two strongly N-conducting areas are diffused in theP-conducting substrate of the semiconductor material (Si). These N-conducting areasare current supplying (“Source”) and current accepting (“Drain”) electrodes. Themetallic gate electrode (in case of the MOSFET), respectively the medium (in case ofthe IsFET), form together with the lower substrate to form a capacitor. A potentialdifference between gate and substrate (Ugs) causes a higher electron density between“Source” and “Drain.” A N-conducting channel is formed, feeding “Source” and “Drain,”a current (Id) is induced.

Measuring principle

1 Metallic gate D Drain2 Channel Ud Drain voltage3 p-doped silicon substrate Ugs Control voltage between gate and sourceS Source Id Drain current

MOSFET

IsFET1 Reference electrode S Source2 Gate isolator layer D Drain3 Medium Ud Drain voltage4 Channel Ugs Control voltage between gate and source5 p-doped silicone substrate Id Drain current6 Isolating layer (TopHit: sensor shaft)

In the IsFET, H+ ions available in the medium, which are located in the medium / gateisolator boundary layer, create the electric field (gate potential). Depending on theeffect described above, a N-conducting channel is formed and a current between“Source” and “Drain” is induced. Suitable sensor circuits use the dependence on theion-selective gate potential to create an output signal proportional to the concentra-tion of the ion type.

Ud

Ugs1

3

2S D

Si (p)

Si (n) Si (n)

Id

Ud

Ugs

1 2 3

5

6

4S D

Si (p)

Si (n) Si (n)

Id

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TopHit CPS 441

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The gate isolator serves as an ion-selective layer for H+ ions. The gate isolator isimpermeable to the ions as well (isolator effect), but allows reversible surfacereactions with the H+ ions. Depending on the acidic or alkaline character of themeasurement solutions, functional groups in the isolator surface accept or reject H+

ions (amphoteric character of the functional groups). This leads to a positive (H+

acceptance in the acidic medium) or negative (H+ rejection in the alkaline medium)charging of the isolator surface. Depending on the pH value, a defined surfacecharge can be used to control the field effect in the channel between “Source” and“Drain.” The processes, which lead to a creation of a charge potential and thereforeto a control voltage Ugs between “Gate” and “Source,” are described with the Nernstequation.

Ugs = U0 +2.3 x RT

nF· Ig(aion)

Ugs = Control voltage between gate and source n = Mol weightU0 = Offset potential F = Faraday constantR = Gas constant aion = activity of ionsT = Temperature (K)

At 68°F (20°C), the Nernst factor is known to have a value of -58 mV/pH.

• Resistance to breakageIts resistance to breakage is the most obvious feature of the sensor. The completesensor is embedded in a PEEK shaft. Only the highly resistant isolator layer andthe reference have direct contact with the medium.• Acidic or alkaline errorsA further important benefit compared to the glass electrode is the considerablyreduced number of acidic or alkaline errors in extreme pH ranges. Compared toglass electrodes, practically no foreign ions can build up at the IsFET gate. Theerror detection limit is < 0.01 pH (between pH 1 and 13 at 77°F). The chart belowshows the acidic or alkali error of the IsFET between pH 1 and 13 and the compari-son to the glass electrode (two different pH glasses) at pH values of 0.09 and 13.86.

2.3 x RT nF

= Nernst factor

Important characteristics of theTopHit CPS 441

pH sensitive IsFet

pH 77°F (25 °C)

DpH

1 M NaOHpH 1 to 131 M HCl-0.2

0.0

0.2

0.4

0.6

0.8

E+H IsFET

Glass 1

Glass 2

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• Isothermic curvesThe Nernst equation (a) defines the dependence of the measuring voltage on thehydrogen ion content (pH value) and the temperature. It is the basis of pH measuringtechnology and for IsFET sensors as well. A temperature-dependent value for thepotential change per pH value can be worked out from this equation (isothermiccurve, potential changes per pH value at a defined temperature). The isothermiccurves of the IsFET sensor are very close to the theoretical values. This is furtherproof for the high pH measurement precision of the TopHit H CPS 491.

Isothermic curves for TopHit CPS 441a = Isothermic curve at 46°F (8°C): slope -55.8 mV/pHb = Isothermic curve at 98°F (37°C): slope -61.5 mV/pHc = Isothermic curve at 142°F (61°C): slope -66.3 mV/pH

• Measurement stability and sensor response timeThe IsFET response times are very short over the whole temperature range. With theIsFET sensor, there is no equilibrium setting (temperature dependent) as in thesource layer of a pH glass of a glass electrode. They can also be used to derive anapplication at low temperatures with a deceleration in response time. Large and fasttemperature and pH value fluctuations have a significantly smaller effect on themeasuring error (hysteresis) than with a glass electrode, as there is no stress exertedon the pH glass.• Reference systemThe integrated reference electrode of the CPS 491 is a double-chamber referencesystem with a bridge electrolyte. The benefits are an efficient and stable contactbetween the diaphragm and the reference lead, and the extremely long poison path.The bridge electrolyte is highly resistant to temperature and pressure changes.

The complete measuring system consists of:• IsFET sensor CPS 441• Measuring cable CPK 12 with TOP 68 connector• Measuring transmitter; Liquisys M CPM 223 (for panel mounting), CPM 253 (for

field mounting), or Mycom S CPM 153• Immersion, flow or retractable holder assembly, e.g. CleanFit P CPA 471 or 475

Additional accessories are available depending on the application:• TopClean S CPC 30 or TopCal S CPC 300 automatic cleaning system• Extension cable, VBA or VBM junction box.

Measuring system

500

300

100

-100

-300

-5000 2 4 6 8 10 12 14 pH

mV

a

bc

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TopHit CPS 441

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Food industries

CPS 491 with TopCal fully automated measuring, cleaning, and calibration system

1 CPS 441 sensor 6 CPG 300 control unit 10 Rinse block2 Retractable holder CPA 475 7 Steam, water, cleaner 11 Electric cable3 CPY 7 KCI electrolyte container 8 Cleaner, buffer solutions 12 Compressed air4 Mycom S CPM 153 transmitter 9 Multihose 13 Liquids/cleaner5 Power supply

Process sterilizing is no problem due to the wide range of applications for the IsFETpH sensor, not only relating to temperature but also pH. There is only a small rangeof extremely high pH values at high temperatures where the sensor is not suitable(see Process conditions). Media with these characteristics remove the isolator oxidefrom the IsFET chip. As this is the pH and temperature range of CIP cleaning media,the CPS 441 should only be used in combination with an automatic retractableholder.Benefits of the TopCal fully automatic measurement, cleaning and calibration system:• CIP cleaing is possible - the sensor built into the retractable holder is automaically

retracted out of the medium before cleaning• Sensor cleaning in the rinse chamber of the retractable holder with suitable

cleaning solutions• Calibration cycles can be individually set• Low maintenance costs due to fully automatic cleaning and calibration functions• Measuring results are optimally reproducable and the individual value tolerances

are very low due to automatic calibration

1 2

3

5

6

78910

111213

4

TopHit CPS 441

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1 CPS 441 electrode2 CPA 442 electrode holder3 KCI electrolyte reservoir4 CPK 12 measuring cable5 Mycom S CPM 153 measuring transmitter

Input

pH value and temperature

0 to 14 pH, 5° to 275°F (-15° to 135°C)Caution!Note the process operating conditions and notes on page 9.

Performance characteristics

Reference temperature, 77°F (25°C)Reference pressure, 14.7 psia (1013 mbar)

< 5 seconds for buffer changes from 4 to 7 pH under reference operating conditions

± 0.2% of measuring range; temperature, Class B according to DIN / IEC 751

± 0.1% of measuring range

Everytime when switching on the measuring device, a control loop is set up. Duringthe this time, the measured value moves to the true value.The setting time depends on the kind of interruption and the interruption time:• Supply voltage interruption, senosr left in process: approximately 3 to 5 minutes• Interruption of the fluid film between pH sensitive IsFet and reference lead:

approximately 5 to 8 minutes• Longer dry storage of the sensor: up to 30 minutes.

Measured values

Measuring ranges

Reference operating conditions

Response time

Maximum measured error

Repeatability

Start-up drift

Biotechnology

1

2

3

45

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TopHit CPS 441

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Measuring cable

Electrical connection

The IsFET TopHit H CPS 441 is connected to the measuring transmitter using theCPK 12 measuring cable.

NOTE: Refer to the transmitter operating instructions for sensor wiring. The transmit-ter specified must be appropriate for the use of IsFET sensors, e.g.Liquisys S CPM 223 / 253. Transmitters with standard pH input only will not workwith the IsFET electrode.

Cable colors yellow and white are connected on the sensor side

RD

Coax cable

GY

Shield

WH

YE

BN

Shield

Source

Drain

Pt1000

Pt1000

Reference

Pt1000

PAL

GND

DRN

SRC (pH)

TopHit CPS 441

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Installation angle IsFET sensors can be installed in any position, as there is no liquid inner seal. In thecase of an overhead installation, a possible air cushion * in the reference systemmight interrupt the electrical contact between the medium and the diaphragm.

* The sensor is shipped without air cushions. Air cushion forming is possible when tanks are cleaned out.

NOTE: The installed sensor may be held under dry conditions for a maximum of 6hours (also applies to overhead installaiton).

Installation

Sensor orientation In principle, IsFET sensors can be installed in any position, as there is no liquid innerlead. When installing the TopHit H CPS 441, note the flow direction of the medium.The IsFET chip should be located at a 45° to the direction of flow (right illustration).The rotating plug-in head of the CPS 441 allows easy installation at a defined angle.

NOTE: Comply with the appropriate operation / installation guidelines for theelectrode holder specified.

1 Endress+Hauser engraving2 Serial number3 Nameplate 1 Endress+Hauser engraving

4 Rotatable part of connection head5 IsFET chip6 Medium flow-past direction

When installing the sensor in a holder, use the engraved serial number on theconnection head for correct sensor orientation. The serial number is always locatedin the same plane as the IsFET chip and the nameplate (z-y direction).In addition, you can use the Endress+Hauser logo engraving for correct sensororientation. The log is rotated by 70 to 90° form the IsFET plane (position 1, righthand graphic above).

z

y

1

2

3

0815

6768

45 °x

zy

1

70-90°

4

x

z

5

6

advised angle of installation

permissible with respect tothe application specific

conditions

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TopHit CPS 441

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Environment

5° to 284°F (-15° to 140°C) The ambient temperature should not drop below 5°F(-15°C). Do not operate the sensor at temperatures below 5°F (-15°C) due to dangerof frost damage.

32° to 122°F (0° to 50°C)

NEMA 6 (IP 68) with TOP 68 plug connector

As with every semiconductor, the IsFET is light-sensitive (fluctuations of measuredvalue). Avoid direct sunlight during calibration and operation. Normal environmentlight does not influence the measurement.

Ambient temperature range

Stroage temperature range

Ingress protection

Sensitivity to light

Process

At high temperatures over a long period of time, alkalis irreversibly destroy the gaeisolator oxide. The sensor can only be used in the indicated range (chart below) at acost of its life span. If it is constantly subjected to the effects of a 2% sodium hydrox-ide solution at 176°F (80°C), the sensor life span drops to approximately 10 to 15hours.

Medium temperature dependingon pH

Temperature and pH

Application range of the sensor according to the order code (see Ordering informa-tion)

Pressure / temperature: 145 psi / max. 212°F (10 bar / 100°C),sterilizable: 43.5 psi / 275°F (3 bar / 135°C) for up to 1 hour

Caution!To prevent damage to the sensor, never use the CPS 441 in applications outside thegiven specifications

Application at low temperatures

248 (120)

212 (100)

176 (80)

140 (60)

104 (40)

68 (20)

32 (0)

0 2 4 6 8 10 12 14 pH

°F (°C)

Restrictedlifetime!

application rangeof

IsFET TopHit

Pressure-temperature diagram

43.5(3)

145(10)

275 (135)

212 (100)

°F (°C)

psi (bar)

Application range of TopHit

TopHit CPS 441

Endress+Hauser10

3.5 ounces (0.1 kg)

Electrode shaft: PEEK, conforms to FDA requirementsEPDM or perfluoroelastomer seals; diaphragm is ceramics

Ra < 0.8 µm (150 grit)

Pt 1000 (Class B to DIN IEC 751)

Pg 13.5

ESB: TOP 68, rotatable

Weight

Materials

Surface roughness

Temperature sensor

Process connection

Plug-in head

Mechanical construction

Dimensions

1 KCI electrolyte connection2 Top 68 plug-in head3 Reference electrode4 IsFET chip5 Seal (EPDM or perflurorelastomer)6 Sensor shaft

Hazardous area approvals

6

3

4

1 2

0.47"(12)

4.72", 8.86”,14.2”, 16.7”(120, 225,360, 425)

4

5

3

Certificates and approvals

FM approved IS, Cl. I, Div. 1, Grps. A-D when used with Mycom S 153-O / -PCSA approved IS, Cl. I, Div. 1, Grps. A-D when used with Mycom S 153-SATEX device group II, Category 1 G; explosion protection EEx iA IIC T4/T6

Sterilizable certified to EHEDG test criteria (TNO Report V3640 RE)Original of report summary“At the request of Endress+Hauser Conducta, Postfach 100154, D-70826 Gerlingen, Germany the in-placecleanability of the ISFET-Sensor TopHit CPS 471 was assessed according to the test procedure of theEuropean Engineering & Design Group (EHEDG).The test results show that the ISFET-Sensor TopHit CPS 471, including the seals, is cleanable in-place at leastas well as the reference pipe. The tests were conducted five times on one test object. The results of thetests are comparable with each other. The ISFET-Sensor TopHit CPS 471 complies with the hygienic criteria ofthe Machinery Directive 98/37/EC, annex 1 (additional essential health and safety requirements for certaincategories of machinery) section 2.1 (agri-foodstuffs machinery), the hygienic requirements of EN 1672 - part2 and with the hygienic equipment design criteria of the EHEDG.The test results obtained are representative of the ISFET-Sensor TopHit type CPS 471 and type CPS 441.”

• Sensor version with EPDM chip seal is hygienic• FDA certified materials

CPS 441 meets the 3-A sanitary standards

Sanitary compatibility

3-A

Endress+Hauser

TopHit CPS 441

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Buffer solutions, accuracy 0.02 pH, according to NIST / DINpH 4.0 red, contents: 3 oz (100 ml) Order No.: CPY 2-0pH 4.0 red, contents: 1qt (1000 ml) Order No.: CPY 2-1pH 7.0 green, contents: 3 oz (100 ml) Order No.: CPY 2-2pH 7.0 green, contents: 1qt (1000 ml) Order No.: CPY 2-3Buffer solutions for single use, accuracy 0.02 pH, according to NIST / DINpH 4.0 red, contents: 0.64 oz (20 x 20 ml) Order No.: CPY 2-DpH 7.0 green, contents: 0.64 oz (20 x 20 ml) Order No.: CPY 2-E

pH buffer solutions

Accessories

Transmitters Liquisys M CPM 223 / 253: pH and ORP transmitter, field or panel mounted housing,for use in hazardous or nonhazardous areas, HART® and PROFIBUS available.Mycom S CPM 153: pH and ORP transmitter, one or two channel version, for use inhazardous or nonhazardous areas, HART® and PROFIBUS available.

TopCal S CPC 300: fully automatic measuring, cleaning and calibration system, foruse in hazardous or nonhazardous areas, in-process cleaning, automatic sensormonitoring.TopClean S CPC 30: fully automatic measuring and cleaning system, for use inhazardous or nonhazardous areas, in-process cleaing, automatic sensor monitoring

Fully automatic measuring systems

Sensor holder assemblies CleanFit P CPA 471: retractable assembly for tank and pipe installationCleanFit P CPA 473: pneumatically or manually driven retractable assembly withball valve for reliable process termination, wetted parts are 316L SSCleanFit P CPA 474: pneumatically or manually driven retractable assembly withball valve for reliable process termination, wetted parts are PP, PEEK or PVDF

CleanFit P CPA 471

CleanFit P CPA 473

CleanFit P CPA 474

CleanFit H CPA 475: retractable assembly for tank and pipe installation under sterileconditionsCleanFit W CPA 111: immersion and installation assembly for open and closed tanksUniFit H CPA 442: installation assembly for food industry, biotechnology and phar-maceutical industry, with 3-A or EHEDG certificate

CleanFit H CPA 475 DipFit W CPA 111 UniFit H CPA 442

United States

Endress+Hauser, Inc.2350 Endress PlaceGreenwood, IN 46143Phone: (317) 535-7138888-ENDRESSFAX: (317) 535-8498

TI 352C/24/ae/09.03© 2003 Endress+Hauser, Inc.

Canada

Endress+HauserCanada Ltd.1440 Graham’s LaneUnit 1, BurlingtonON, L7S 1W3Phone: (905) 681-9292800-668-3199FAX: (905) 681-9444

Mexico

Endress+HauserPaseo del Pedregal No. 610Col. Jardines del Pedregal01900, Mexico D.F.MexicoPhone: (525) 568-2405FAX: (525) 568-7459

For application and selection assistance,in the U.S. call 888-ENDRESS

For total support of your installed base, 24 hoursa day, in the U.S. call 800-642-8737

Visit us on our web site, www.us.endress.com

1 2 3TopHit H CPS 441 sensor

CPS 441 -

1 Shaft length2 4.7” (120 mm) shaft length4 8.9” (225 mm) shaft length5 14.2” (360 mm) shaft length6 16.7” (425 mm) shaft length

2 Terminal headESS Threaded plug-in head, Pg 13.5, TOP 68 connection, rotatable

3 Options1 Chip seal: EPDM, hygienic2 Chip seal: Perfluoroelastomer9 Special version according to customer specification

Ordering information

CPK 12 measuring cable CPK 12 -

1 Cable lengthHA 16 ft (5 m), TPE sheath, max. 266°F (130°C)HB 33 ft (10 m), TPE sheath, max. 266°F (130°C)HC 50 ft (15 m), TPE sheath, max. 266°F (130°C)HD 65 ft (20 m), TPE sheath, max. 266°F (130°C)HE 82 ft (25 m), TPE sheath, max. 266°F (130°C)HF 5 to 20 m (sold in m lengths), TPE sheath, max. 266°F (130°C)HG 16 to 65 ft (sold in ft lengths), TPE sheath, max. 266°F (130°C)HH 10 ft (3 m), TPE sheath, max. 266°F (130°C)NA 16 ft (5 m) PVC sheath, max. 176°F (80°C)

2 VersionA Standard applications, black sheathZ Hazardous applications, Blue sheath

3 Wire termination1 End sleeve on device side, braided cable shielding

4 Ground connectionA External potential matching with flat plug

1 2 3 4

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Supplemental documentation

Cleanfit P CPA 471 Technical Information, TI 217C/24/aeCleanfit P CPA 473 Technical Information, TI 344C/24/aeCleanfit P CPA 474 Technical Information, TI 345C/24/aeCleanfit H CPA 475 Technical Information, TI 240C/24/aeDipFit W CPA 111 Technical Information, TI 112C/24/aeDipFit P CPA 140 Technical Information, TI 178C/24/aeUniFit H CPA 442 Technical Information, TI 297C/24/ae

Liquisys S CPM 223/253 Technical Information, TI 194C/24/aeMycom 153 Technical Information, TI 233C/24/ae

TopClean Technical Information, TI 235C/24/aeTopCal Technical Information, TI 236C/24/ae

Measuring cable CPK 1-12 Technical Information, TI 124C/07/en

Transmitters

Fully automatic systems

Measuring cable

Holder assemblies