ENDRESS+HAUSER  CPS471D-721C

Sterilizable and autoclavable ISFET sensor for the pH measurement Analog or digital sensors with Memosens technology

• Hygienic and sterile applications
• Food industry and pharmaceutical industry
• Biotechnology

• Resistant to breaking
  • Sensor body made completely of PEEK
  • Direct installation into the process, reduces effort and costs for sampling and laboratory analysis
• Certified biocompatibility
• Double-chamber reference system:
  • poisoning resistant
  • polyacrylamide free gel
• Application possible at low temperatures
  • Short response time
  • Constantly high accuracy
• Sterilizable and autoclavable
• 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 for effective temperature compensation
• Ideal for CIP processes when combined with an automatic retractable assembly

• Maximum process safety through contactless inductive signal transmission
• Data safety through digital data transmission
• Easy handling thanks to storage of sensor-specific data in the sensor
• Predictive maintenance possible thanks to registration of sensor load data in the sensor

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

Ion-selective field effect transistors use an MOS 1) transistor arrangement (see Fig 1) where the metallic gate (pos. 1) is not a control electrode. Instead, the medium (see Fig 2, pos. 3) in the ISFET is in direct contact with the gate isolator layer (pos. 2).Two strongly N-conducting areas are diffused in P-conducting substrate (see Fig 2, pos. 5) of the semiconductor material (Si). These N-conducting areas are current supplying ("Source", S) and current accepting ("Drain", D) electrodes. The metallic gate electrode (in case of the MOSFET) resp. the medium (in case of the ISFET) forms a capacitor with the substrate below. A potential difference between gate and substrate (U GS ) causes a higher electron density between "Source" and "Drain". A N-conducting channel (pos. 2) is formed, i.e. a drain current (I D ) is induced.

With the ISFET, the medium is in direct contact with the gate isolator layer. Therefore, H + ions available in the medium, which are located in the medium / gate isolator boundary layer, create the electric field (gate potential). Depending on the effect described above, a N-conducting channel is formed and a current between "Source" and "Drain" is induced. Suitable sensor circuits use the dependence on the ion-selective gate potential to create an output signal proportional to the concentration of the ion type.

The complete measuring system comprises at least:

• ISFET sensor Tophit
• Measuring cable CPK12 (analog, with TOP68 connection) or CYK10 (digital, with Memosens)
• Transmitter, e.g. Liquiline CM4x, Liquisys CPM223 (for panel mounting) or Liquisys CPM253 (field instrument) or Mycom CPM153.
• Assembly
  • Immersion assembly, e.g. Dipfit CPA111
  • Flow assembly, e.g. Flowfit CPA250
  • Retractable assembly, e.g. Cleanfit CPA471 (CPA450 only with CPS471D, CPS491D or special versions CPS471-ESA and CPS491-ESA, --> Ordering information)
  • Fixed installation assembly, e.g. Unifit CPA442

There are additional accessories available depending on the application:

• Topclean CPC30 or Topcal CPC310 automatic cleaning system
• Extension cable, VBA, VBM or RM junction box