Ohaus pH Meter

Description

After more than a century of perfecting the art of measurement through our durable weighing products, OHAUS precision is now available in a line of pen meters that provide accurate measurement of pH, oxidation-reduction potential (ORP), conductivity, salinity, and total dissolved solids (TDS). Starter pen meters are the economical option when you are simply looking for meters that will provide accurate measurement without restriction. pH Meter Supplier in Bangladesh

Applications	pH, oxidation-reduction potential (ORP), conductivity, dissolved oxygen (DO), salinity, total dissolved solids (TDS), temperature measurement
Display	Liquid crystal display (LCD) display with secondary information line (on select models)
Operation	4 1.5V batteries (included)
Communication	N/A pH Meter Supplier in Bangladesh
Construction	ABS Housing
Design Features	Easily replaceable electrodes, automatic shut off feature

pH Meter Supplier in Bangladesh

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Full form of pH Meter Supplier in Bangladesh

The full form of pH is “Potential of Hydrogen”. pH is known as the negative logarithm of H+ ion concentration. Hence the meaning of the name pH is explained as the strength of hydrogen or power of hydrogen. pH describes the concentration of the hydrogen ions in a solution, which is the indicator of the acidity or basicity of the solution. The pH value on a pH scale varies from 0 to 14. pH Meter Supplier in Bangladesh

pH of Acid And Base

The pH of the solution ranges from 0 to 14.

Solutions with a pH value varying from 0 to <7 on the pH scale are called acidic solutions.

Solution with a pH value ranging from >7 to 14 is known as basic solutions.

Importance of pH Meter Supplier in Bangladesh

A living organism can withstand only a limited range of pH changes, and any more pH adjustments will make life difficult. For example: in the case of acid rain, the pH of the water is less than 7. It decreases the pH of river water as it flows into a river which hinders the survival of marine life.

The human stomach lining secretes hydrochloric acid, which helps digest food by activating certain enzymes. Antacids are used to neutralize the acid produced in the stomach in case of acid reflux. Antacids are used to neutralize the acid produced in the stomach in case of acid reflux.

Often the bacteria present in our mouth lower the pH of our mouth by generating acids through food particle degradation. This results in the demineralization of teeth and tooth decay. Therefore, we are told to clean our teeth and mouths since mouthwash neutralizes the acid and helps in remineralization. Fluoride toothpaste aids in remineralization and prevents decay.

In the case of a bee sting, we feel a lot of pain when the bee injects formic acid (methanolic acid) through its sting.

pH Measurement

A very important measurement in many liquid chemical processes (industrial, pharmaceutical, manufacturing, food production, etc.) is that of pH: the measurement of hydrogen ion concentration in a liquid solution. A solution with a low pH value is called an “acid,” while one with a high pH is called a “caustic.” The common pH scale extends from 0 (strong acid) to 14 (strong caustic), with 7 in the middle representing pure water (neutral):

pH is defined as follows: the lower-case letter “p” in pH stands for the negative common (base ten) logarithm, while the upper-case letter “H” stands for the element hydrogen. Thus, pH is a logarithmic measurement of the number of moles of hydrogen ions (H+) per liter of solution. pH is defined as follows: the lower-case letter “p” in pH stands for the negative common (base ten) logarithm, while the upper-case letter “H” stands for the element hydrogen. Thus, pH is a logarithmic measurement of the number of moles of hydrogen ions (H+) per liter of solution.

The logarithmic pH scale works like this: a solution with 10-12 moles of H+ ions per liter has a pH of 12; a solution with 10-3 moles of H+ ions per liter has a pH of 3. While very uncommon, there is such a thing as an acid with a pH measurement below 0 and a caustic with a pH above 14.

pH Electrodes

While pH can be measured by color changes in certain chemical powders (the “litmus strip” is a familiar example from high school chemistry classes), continuous process monitoring and control of pH requires a more sophisticated approach. The most common approach is the use of a specially-prepared electrode designed to allow hydrogen ions in the solution to migrate through a selective barrier, producing a measurable potential (voltage) difference proportional to the solution’s pH:

The design and operational theory of pH electrodes is a very complex subject, explored only briefly here. What is important to understand is that these two electrodes generate a voltage directly proportional to the pH of the solution. At a pH of 7 (neutral), the electrodes will produce 0 volts between them.

Reference Electrode

The other electrode (called the reference electrode) is made from a chemical solution of neutral (7) pH buffer solution (usually potassium chloride) allowed to exchange ions with the process solution through a porous separator, forming a relatively low resistance connection to the test liquid. At first, one might be inclined to ask: why not just dip a metal wire into the solution to get an electrical connection to the liquid? The reason this will not work is that metals tend to be highly reactive in ionic solutions and can produce a significant voltage across the interface of metal-to-liquid contact.

The use of a wet chemical interface with the measured solution is necessary to avoid creating such a voltage, which of course would be falsely interpreted by any measuring device as being indicative of pH Meter Supplier in Bangladesh

Here is an illustration of the measurement electrode’s construction.

Here is an illustration of the reference electrode’s construction. The porous junction shown at the bottom of the electrode is where the potassium chloride buffer and process liquid interface with each other:

The measurement electrode’s purpose is to generate the voltage used to measure the solution’s pH. This voltage appears across the thickness of the glass, placing the silver wire on one side of the voltage and the liquid solution on the other.

pH Meter Supplier in Bangladesh

While the reference electrode’s connection to the test liquid may only be a few kilo-ohms, the glass electrode’s resistance may range from ten to nine hundred mega-ohms, depending on electrode design! Being that any current in this circuit must travel through both electrodes’ resistances (and the resistance presented by the test liquid itself), these resistances are in series with each other and therefore add to make an even greater total.

While the reference electrode’s connection to the test liquid may only be a few kilo-ohms, the glass electrode’s resistance may range from ten to nine hundred mega-ohms, depending on electrode design! Being that any current in this circuit must travel through both electrodes’ resistances (and the resistance presented by the test liquid itself), these resistances are in series with each other and therefore add to make an even greater total.

An ordinary analog or even digital voltmeter has much too low of internal resistance to measure voltage in such a high-resistance circuit. The equivalent circuit diagram of a typical pH probe circuit illustrates the problem:

Even a very small circuit current traveling through the high resistance of each component in the circuit (especially the measurement electrode’s glass membrane). Will produce relatively substantial voltage drops across those resistances. Seriously reducing the voltage seen by the meter. Making matters worse is the fact that the voltage differential generated by the measurement electrode is very small. In the millivolt range (ideally 59.16 millivolts per pH unit at room temperature). The meter used for this task must be very sensitive and have an extremely high input resistance.

Measurement Problem

The most common solution to this measurement problem is to use an amplified meter with an extremely high internal resistance to measure the electrode voltage. So as to draw as little current through the circuit as possible. Another approach, seldom seen in contemporary use, is to use a potentiometric “null-balance” voltage measurement setup to measure. This voltage without drawing any current from the circuit under test. If a technician desired to check the voltage output between a pair of pH electrodes. This would probably be the most practical means of doing so using only standard benchtop metering equipment:

This would probably be the most practical means of doing so using only standard benchtop metering equipment:

With the detector “nulled” (registering exactly zero). There should be zero current in the pH electrode circuit. And therefore no voltage dropped across the resistances of either electrode. Giving the real electrode voltage at the voltmeter terminals.

Wiring requirements for pH electrodes tend to be even more severe than thermocouple wiring. Demanding very clean connections and short distances of wire (10 yards or less. Even with gold-plated contacts and shielded cable) for accurate and reliable measurement.

Few instrumentation technologies inspire the awe and mystique commanded by pH measurement. Because it is so widely misunderstood and difficult to troubleshoot. Without elaborating on the exact chemistry of pH measurement. And. So so. And. So so. And. So so

pH Measurement Systems:

1. All pH electrodes have a finite life, and that lifespan depends greatly on the type and severity of service. In some applications, a pH electrode life of one month may be considered long, and in other applications, the same electrode(s) may be expected to last for over a year.
2. Because the glass (measurement) electrode is responsible for generating the pH-proportional voltage. It is the one to be considered suspect if the measurement system fails to generate sufficient voltage change for a given change in pH (approximately 59 millivolts per pH unit). Or fails to respond quickly enough to a fast change in test liquid pH. And. So so. And. So so. And. So so
3. If a pH measurement system “drifts,” creating offset errors, the problem likely lies with the reference electrode.
4. Because pH measurement is a logarithmic representation of ion concentration. Also, due to the nonlinear nature of the logarithmic scale. A change of 1 pH at the top end (say, from 12 to 13 pH) does not represent. The same quantity of chemical activity change as a change of 1 pH at the bottom end (say, from 2 to 3 pH). Control system engineers and technicians must be aware of this dynamic. If there is to be any hope of controlling process pH at a stable value.
5. The following conditions are hazardous to measurement (glass) electrodes: high temperatures, extreme pH levels (either acidic or alkaline). High ionic concentration in the liquid, abrasion, hydrofluoric acid in the liquid (HF acid dissolves glass!). And any kind of material coating on the surface of the glass.

REVIEW: pH Meter Supplier in Bangladesh

pH is a representation of hydrogen ion activity in a liquid. It is the negative logarithm of the number of hydrogen ions (in moles) per liter of liquid. Thus: 10-11 moles of hydrogen ions in 1 liter of liquid = 11 pH. 10-5.3 moles of hydrogen ions in 1 liter of liquid = 5.3 pH. And. So so. And. So so. And. So so
The basic pH scale extends from 0 (strong acid) to 7 (neutral, pure water) to 14 (strong caustic). Chemical solutions with pH levels below zero and above 14 are possible but rare. And. So so. And. So so. And. So so
It’s a job is to generate a small voltage proportional to pH (ideally 59.16 mV per pH unit). And. So so. And. So so. And. So so
The other electrode (called the reference electrode) uses a porous junction between the measured liquid and a stable. Neutral pH buffer solution (usually potassium chloride) to create a zero-voltage electrical connection to the liquid. This provides a point of continuity for a complete circuit. So that the voltage produced across the thickness of the glass. And. So so. And. So so. And. So so