7.8. pH METER

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'Informatics in practice' may not mean very costly systems or devices. True, there are very expensive, but very affordable priced and not so great for overall dimensions. One example is the 'Seven Easy pH Meter' firm METTLER TOLEDO. pH meter is sensory devices for measuring the acidity of a solution that measures the concentration of hydrogen ions in them i.e. pH. Serves as an electrical sensor glass membrane which has a certain thickness, and in which when set between two electrolyte ion exchange on both sides of the membrane. In this case it comes to the appearance of the potential difference between two solutions separated by a glass dome which in turn depends on the concentration of hydrogen ions. If the concentration in solution is constant, then the potential difference depends on the concentration of hydrogen ions in the second solution. Favorable electrical meter amplifiers measure the potential of glass electrode is dependent on the concentration of H+ ions. Although the instruments called pH meters are not limited only to the determination of the concentration of H+ ions. Elements or compounds which are determined solely depend on potentiometric sensor that is on used indicator electrode.

Manner of its use is shown in the following figure, a glass cup in which the electrode is best illustrated by its size. The instrument has a separate power adapter, and can operate on batteries.

 pH meter
Figure 7.8.1 Basic components of 'Seven Easy' measurement system.

In the left corner of the image shows the ports used. There is a port for an external power supply, connection to the electrode and ATC connector when using electrodes with built-in or remote temperature 'probe', and the DB9 connector type to send data to the computer. Display of 'Liquid Crystal' technology, which now has almost every hour or cell phone, shows about 13 different data sets or incurred during the measurement.

 Display of pH meter  
Figure 7.8.2 Display of the measuring system.    

The most important of these are:

Part of the technical specifications in the factory instructions shown again:

         -----------------------------------------------------------
         Unit               :      pH           mV          °C
         Measurement Range  : 0.00 - 14.00   ± 1999      (-5)-(+105)
         Resolution         :     0.01           1          0.1
         Relative Accuracy  :   ± 0.01         ± 1        ± 0.5

         pH-calibration     : 1, 2, or 3 points 
         Isopotential Point : 7.00 pH

         Outputs: RS 232 serial
           Baud rate : 1200
           Data bit  : 8
           Stop bit  : 1
           Parity    : none

         pH Input    : Combination electrode
         Impedance   : > 1'000'000'000'000 Ω (ohm)

         Size/Weight : 180 × 180 × 65 mm / 0.61 kg

         Material
         Casing             :  ABS, PC enforced
         Electrode stand    :  ABS, PC enforced
         Membrane keypad    :  Polyester

         Power Requirements :  230V/50 Hz, 10 VA, 9 V DC
         -----------------------------------------------------------

The basic electrical characteristics of what should be noted is a small data rate and a very high input impedance of the terminal electrodes. The reason for this is the elimination of the impact of electronic devices on the course and results of the measurements, because of such a high input impedance input through the electronic circuit of the instrument does not pass almost no current. To make the computer accepted and deposited the instrument sends data to the parameters set by the previous speed serial RS 232 port, and a program that monitors aid. This could be some kind of very expensive software support that will be able to read, store data, analysis, graphics and the like and may be used and simplest TELNET program support which the parameters are set as shown below.

 Settings for measurement
Figure 7.8.3 Setting parameters of TELNET program.

If the computer and the instrument parameters are not agreed not to receive any view or will be unreadable. As there is no indication in the particular specifications, data exchange is done in ASCII code. The following figure shows how the user is allowed to take data from the instrument are saved to file MARIO.TRM. Figure 4.2.3 shows a group of 'Accessories', which was launched from the TERMINAL application and that before accepting the data must be set the parameters for the computer to communicate with the instrument.

 Results of measurement
Figure 7.8.4 Reading of TERMINAL window.

Data are presented in three columns. Show basic pH measured value. As the speed of data exchange only about a hundred characters per second, it is a slow track changes in the chemical process. What data obtained? Everything that he wants. They can be transferred to Excel on Windows XP/Vista/7 platforms, process and analyze or in some other professional program of profession.

It may be noted that the data files are marked by the principle NAME.TYPE, which is specific for the DOS operating system. It should nevertheless be familiar with the basics of a computer. If you are using a DOS-Windows operating systems should always keep in mind the image specification is shown in Chapter 4.1.1. The difference compared to newer types of 'window' was later used as file names up to 32 characters, but kept for compatibility and shorter, so the example folder (directory) [C:\MY- MEASUREMENT\] in Windows XP or Windows 7 operating system, displayed as [C:\MY-MEA~1\] if the data is transferred to the Windows 3.11 operating system. Therefore, in such cases, make sure that the file names are understandable and no more than eight characters because of how quickly distinguished as [C:\MY-MEA~1\], [C:\MY-MEA~2\] or [C:\MY-MEA~3\]. Despite all the beauties offered by newer Microsoft operating systems not advisable to forget the 'good old DOS', at least some of its basic settings and commands that XP/Vista/7 and is used in the 'Command Prompt' window.




SUMMARY:

Take a look at the last two pictures, it is evident that these icons of Windows 3.11 OS. Thus, the operating system that can no longer be developing long nor products, but is normal in today's terms at a very modest computers. In this case, the type of computer is xx386 with 8 MB of RAM and disk capacity of about 100 MB.

Nevertheless one stylish device uses very undemanding computing resources and can efficiently serve a purpose: measuring the pH of a solution. So, do not 'throw' old computers and OS as they can effectively serve despite obsolescence. Low cost and reliability of these devices make them ideal for environmental monitoring in order to face up to the time of climate change that we follow.

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Citing this page:
Radic, Drago. " IT - Informatics Alphabet " Split-Croatia.
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