If there is more hydrogen ion activity in the blue solution, it's more acidic than the orange solution and the meter shows this as a lower pH; in the same way, if there's less hydrogen ion activity in the blue solution, the meter shows this as a higher pH (more alkaline).
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If you're using litmus paper, none of this matters. The basic idea is that the paper turns a slightly different color in solutions between pH 1 and 14 and, by comparing your paper to a color chart, you can simply read off the acidity or alkalinity without worrying how many hydrogen ions there are. But a pH meter somehow has to measure the concentration of hydrogen ions.
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What the glass electrode does is to measure the difference in pH between the orange solution and the blue solution by measuring the difference in the voltages their hydrogen ions produce. Since we know the pH of the orange solution (7), we can figure out the pH of the blue solution.
http://www.explainthatstuff.com/how-ph-meters-work.html
Best Answer: A glass electrode creates a current which is read by a pH meter. A common glass electrode for measuring hydrogen ion concentration in a solution utilizes a special type of glass which is very thin.
https://answers.yahoo.com/question/index?qid=20080519161242AAtVuUa
Their concentration determines the current produced by the probe which is measured by the meter. The greater the hydrogen ion concentration, the greater the current produced by the probe. http://www.sensorex.com/support/educatio... A pH meter is used to measure the acidity of a solution. As I'm learning in Chemistry now, H+ ions are responsible for making acids. On a pH meter, 0-6.9 is an acid, 7 is neutral, and 7.1-14 is considered a base. A base, for your extra knowledge, has a high concentration of OH- ions. Anyways, a standard pH meter usually has a probe sticking into the solution hooked up to the machine.
https://answers.yahoo.com/question/index?qid=20080519161242AAtVuUa
How a pH meter works. To be able to measure pH one needs to have a ph meter which is sensitive to the hydrogen ions that define the pH value. The principle of the measurement is that one takes a sensor with a glass membrane which is sensitive to hydrogen ions and observes the reaction between it and a sample solution.
http://www.labpro.co.uk/phmeters/technical-web/how-a-phmeter-works.php
How do ORP (oxidation reduction potential) meters work? In very simple terms, I'd like to understand how the device measures the electrical potential of the water. Is it measuring the actual power of the water in millivolts? Is sanitized water like a battery, or does the ORP meter create a battery by placing two different metals (silver and platinum) in the water?
https://www.quora.com/How-do-ORP-oxidation-reduction-potential-meters-work
A typical pH meter has two basic components: the meter itself, which can be a moving-coil meter (one with a pointer that moves against a scale) or a digital meter (one with a numeric display), and either one or two probes that you insert into the solution you're testing.
http://www.explainthatstuff.com/how-ph-meters-work.html
This potential is a linear function of the hydrogen concentration in the solution, which allows quantitative measurements to be made. Figure 1 shows a pH meter measurement setup with two separate sensors, a pH sensor and a reference sensor is shown. Nowadays, ph meters merge the two separate sensors into one electrode.
http://www.labpro.co.uk/phmeters/technical-web/how-a-phmeter-works.php
An ORP meter is measuring the activity of oxidizing or reducing contaminants in the water such as Chlorine, Iron . The water itself is just the solvent for these contaminants. The ORP reading is made by, as you say, effectively creating a battery and measuring the voltage produced. Reduction potential.
https://www.quora.com/How-do-ORP-oxidation-reduction-potential-meters-work
how do ph meters work
To use Potential of Hydrogen meters, one takes a sensor with a glass membrane which is sensitive to hydrogen ions and observes the reaction between it and a sample solution.   The principle of the pH meter measurement is that one takes a sensor with a glass membrane which is sensitive to hydrogen ions and observes the reaction between it and a sample solution.