SENTRON A120-001,A120-002,A120-003,A120-004,A120-005 Technical Manual
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ISFET pH-sensor kit
Technical guide
Contents
Description..................................................................................................................................2
Specifications ..............................................................................................................................3
Electrical connections..................................................................................................................4
3.1 Analog front-end module.....................................................................................................4
3.2 AD Converter module ..........................................................................................................4
3.3 USB Interface module ..........................................................................................................5
Calibration ..................................................................................................................................6
Data communication ...................................................................................................................7
5.1 Protocol ...............................................................................................................................7
5.2 Examples .............................................................................................................................8
5.2.1 Performing a single point calibration ............................................................................8
5.2.2 Performing a multi-point calibration ............................................................................9
5.2.3 Retrieving the pH signal ............................................................................................. 10
5.2.4 Retrieving the temperature signal .............................................................................. 10
5.2.5 Retrieving the slope values ........................................................................................ 11
5.3 ASCII table ......................................................................................................................... 12
E7500347.02
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Description
Sentron offers a glass-free modular pH-kit designed specifically for development and testing
purposes. With this pH-kit, development engineers and researchers have a large degree of flexibility
in how they integrate our proprietary ISFET pH sensor into their applications or experimental set-ups.
Due to the modular design, the functionality can be expanded as required and components can be
replaced individually.
The pH-kit consist of a ISFET pH sensor, Reference and Analog front-end module. These modules are
always needed as a basis for pH measurement. Thanks to the small size of the ISFET pH sensor and
Reference electrode it can be used to measure small volumes or develop applications with small
form factors. The Analog Front-end module has an uncalibrated analog pH output signal with a
voltage output 0 — 3.3 V of ~ 52 mV / pH and pH 7 between 500 mV and 1800 mV. The PT1000 RDT
temperature sensor in the ISFET pH sensor is wired directly to the Analog front-end module output.
The reference electrode also connects to the Analog front-end module and either the standard
reference electrode with porous PTFE diaphragm can be used or a suitable custom reference
electrode can be attached.
The AD Converter module can be attached to the Analog front-end module. This extension module
with microprocessor, AD Converter and galvanic isolation makes it well suited for use in embedded
applications. The communication with the AD Converter is based on a serial RS232 interface with a
TTL level. Using a standard serial interface it is possible to perform calibrations and read pH and
temperature values. Application of a temperature correction algorithm to the pH signal is performed
directly by the microcontroller of the AD Converter module. The galvanic isolation provides an extra
safety barrier and prevents ground loops.
With the USB Interface extension module, which connects to the AD Converter module, it is possible
to request measured pH and temperature values from a laptop or PC with a USB port. The USB
Interface extension module, with appropriate user developed software, allows the pH-kit to be used
for applications that require direct connection to a PC, such as real time monitoring of pH values in
an experiment or process.
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Specifications
4
Electrical connections
The diagram below illustrates how the components of the pH-kit are connected together. The
modules will only function when connected in this order.
1. ISFET sensor +
Reference electrode
2. Analog front-end
3. AD Converter
(Optional)
4. USB Interface
(Optional)
Modules 1 and 2 are always needed to conduct pH measurements with the test kit. Modules
3 and 4 are optional.
3.1 Analog front-end module
The ISFET sensor is connected to the Analog Front-End module through an FFC connector. There are
also 7 pin connections on the module. One pin (Pin 7) is for connection of the reference electrode.
The remaining 6 serve as output pins for the Analog front-end module. They are described below:
7.
Pin 1. pH signal out ~52 mV/pH. pH 7 between 500 and 1800 mV
Pin 2. +3V3 Power +3V3 DC power power input +/- 100mV
Pin 3. AGND Analog Ground
Pin 4. PT1000 Directly wired to the PT1000
Pin 5. PT1000 Directly wired to the PT1000
Pin 6. N.C. Not used
Pin 7. Reference External reference electrode connection
3.2 AD Converter module
The 6 pin connector of the AD Converter module can be attached directly to the Analog Front-end
module. The AD Converter module also had 4 output pins, which are described below:
Pin 1. +5V +5V DC power input +/- 100mV
Pin 2. RxD Data input, TTL 5V level, 115k2, 8N1
Pin 3. TxD Data output, TTL 5V level, 115k2, 8N1
Pin 4. GND Digital GND.
The AD Converter module contains 1.5kV galvanic insulation between inputs and outputs.
1.
2.
3.
4.
1.
2.
3.
4.
5.
6.
ISFET
sensor
connector
Analog
front-end
connector
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