Endress+Hauser CPS47D Specifications

TI01412C/07/EN/01.18 71425017 2018-07-09

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Memosens CPS47D

Sterilizable and autoclavable ISFET sensor for pH measurement Digital with Memosens technology

Application

Special applications for:

• Highest accuracy

• Clogging media (pressurized)

• High concentration of organic solvents

• Low conductivities

Your benefits

• Break-resistant – Sensor body made entirely of PEEK (FDA compliant) – Can be installed directly in the process, saving time and cost for sampling and

laboratory analysis

• Refillable KCI liquid electrolyte

• Operation at low temperatures – Short response time – Consistently high accuracy

• Sterilizable

• Longer calibration intervals than with glass electrodes – Shorter hysteresis in event of temperature change – Smaller measuring errors following exposure to high temperatures – Virtually no acid and alkaline errors

• Integrated temperature sensor for effective temperature compensation

• Improved alkaline stability

• Ideally suited for CIP processes when combined with an automatic retractable assembly

Advantages offered by Memosens technology

• Maximum process safety thanks to non-contact, inductive signal transmission

• Data security thanks to digital data transmission

• Very easy to use as sensor data saved in the sensor

• Predictive maintenance possible as sensor load data are recorded in the sensor

• Heartbeat

Function and system design

Si (n)

Si (p)

Si (n)

Si (p)

Memosens CPS47D

Measuring principle

Ion-selective, or more generally, ion-sensitive field effect transistors (ISFET) were developed in the 1970s as an alternative to glass electrodes for pH measurement.

General principles

Ion-selective field effect transistors are based on an MOS

transistor arrangement →  1,  2. Unlike the MOS, however, the ISFET sensor does not have a metal gate (item 1) as the control electrode. Instead, in the ISFET sensor →  2,  2 the medium (item 3) is in direct contact with the gate insulator layer (item 2). Two highly p-conducting regions are diffused into the n-conducting substrate material (item 5) of the semi-conductor (Si). They act as the charge-supplying electrode ("Source", S) and the charge-accepting electrode ("Drain", D). The metal gate electrode (in the case of the MOSFET) and the medium (in the case of the ISFET) forms a capacitor with the underlying substrate. A difference in potential (voltage) between the gate and substrate (UGS) increases the electron density in the area between the "Source" and "Drain". A conductive channel forms →  2,  2(item 4), such that a current ID flows when a voltage UD is applied.

A0036074

 1 MOSFET principle

1 Metal gate 2 Conductive channel (N-conducting)

 2 ISFET principle

1 Reference electrode 2 Gate insulator layer 3 Medium 4 Conductive channel (N-conducting) 5 N-doped silicon substrate 6 Sensor shaft

A0003856

With the ISFET, ions that are in the medium and located in the boundary layer between the medium/gate insulator generate the electric field (gate potential). The effect described above causes a conductive channel to form in the silicon semi-conductor substrate between the "Source" and "Drain", and causes current to flow between the "Source" and "Drain".

Suitable sensor circuits use the dependence of the ion-selective gate potential to generate an output signal that is proportional to the concentration of the ion type.

pH-selective ISFET

The gate insulator acts as an ion-selective layer for H+ ions. While the gate insulator is also impermeable to these ions (insulator effect), it allows reversible surface reactions with H+ ions. Depending on the acidic or alkaline character of the medium, functional groups in the insulator surface either accept or donate H+ ions (amphoteric character of the functional groups). This results in positive charging at the insulator surface (H+ ions accepted in the acidic medium) or negative charging at the insulator surface (H+ ions donated in the alkaline medium). Depending on the pH value, a defined surface charge can be used to control the field effect in the channel between the

1) Metal Oxide Semiconductor

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Memosens CPS47D

"Source" and "Drain". The processes which lead to the creation of a charge potential and therefore to a control voltage UGS between the "Gate" and "Source" are described by the Nernst equation:

Measuring system

UGS = U0 +

R Gas constant (8.3143 J/molK) 2.3 . RT T Temperature [K] n Valency (1/mol)

2.3 . RT

Potential between gate and source F Faraday constant (26.803 Ah) Offset voltage a

lg a

ion

Activity of ion type (H+)

Nernst factor

At 25 °C (77 °F) the Nerst factor of the pH measurement has the value -59.16 mV/pH.

The complete measuring system comprises at least:

• ISFET sensor

• Memosens data cable: CYK10 (Memosens, digital sensor)

• Transmitter, e.g. Liquiline CM44, Liquiline CM42

• Assembly – Immersion assembly, e.g. Dipfit CPA111 – Flow assembly, e.g. Flowfit CPA250 – Retractable assembly, e.g. Cleanfit CPA875 or CPA871 – Permanent installation assembly, e.g. Unifit CPA842

Additional options are available depending on the application: Automatic cleaning and calibration system, e.g. Liquiline Control CDC90

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Food industry

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Memosens CPS47D

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 3 Complete measuring system

1 Water connection, at installation location 2 Assembly 3 KCI supply vessel CPY7B 4 Process/medium 5 Rinsing block 6 Pump canister unit 7 Pneumatic control unit 8 CDC90 control unit 9 Ethernet switch 10 Media (cleaners, buffers) 11 Compressed air line 12 Electric cable, signal cable

For detailed information on Liquiline Control CDC90: Operating Instructions BA01707C, Technical Information TI01340C

As the ISFET sensor can be used in a broad range of applications - both with regard to temperature and the pH value - sterilization in place (SIP) is not a problem. There is only a small range involving high pH values in combination with high temperatures where the sensor's long-term stability is somewhat compromised. Media with such properties reduce the insulator oxide of the ISFET chip. As this is the pH and temperature range of CIP cleaning media, the ISFET sensor is only used here in combination with an automatic retractable assembly.

Advantages of the CDC90 fully automated cleaning and calibration system:

• Cleaning in place (CIP): The sensor in the retractable assembly is automatically retracted from the medium for the duration of the alkaline phase or for the entire CIP process. The sensor is then rinsed with a suitable cleaning agent in the rinse chamber.

• Calibration cycles can be set individually

• Reduced maintenance thanks to fully automated cleaning and calibration

• Optimum reproducibility of the measurement results

• Very low individual value tolerances thanks to automatic calibration

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Memosens CPS47D

Pharmaceutical industry and biotechnology

A0037989

 4 Measuring system for pharmaceutics and biotechnology

1 ISFET sensor 2 Installation assembly Unifit CPA842 3 Memosens data cable CYK10 4 Liquiline CM42 transmitter 5 KCI supply vessel CPY7B

Properties

Acid or alkaline errors Another important advantage over the glass electrode is the lower acid or alkaline errors in extreme pH ranges. In contrast to the glass electrode, almost no foreign ions can build up at the ISFET gate. Between pH 1 and pH 13, the measured error averages Δ pH 0.02 (at 25 °C (77 °F)) and is therefore at the detection limit. The following graphic shows the average measured error of the ISFET sensor in the pH 1 to 13 range compared with two glass electrodes (2 different pH glasses) at the extreme values of pH 0.09 (1 M HCl) and 13.86 (1 M NaOH).

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