What Is a Potometer?
A potentiometer is an instrument constructed using the principle of compensation. High-precision measuring instrument based on the principle of mutual compensation between the measured voltage and the known voltage. There are two types of AC and DC. Used to measure voltage, current, and resistance. AC potentiometers also measure magnetism.
- Also known as potentiometer, potentiometer. An instrument based on the principle of mutual compensation (ie, balance) between the measured voltage and the known voltage. Compared with voltmeters, the main advantage is that the circuit under test does not need to supply current during measurement, so it does not affect the circuit under test, and it can accurately measure the power emf. Generally there are two types: rotary handle type and sliding line type.
- Since the potential compensation method is used, the measurement accuracy is high. It avoids the error caused by the internal resistance of the power supply, and measures its voltage at the end of the circuit without current passing through the power supply, which greatly improves the accuracy and sensitivity [1]
- When no current flows, the potential difference between the positive and negative electrodes of the battery is equal to the electromotive force of the battery. If current flows, because
- There are many types of potentiometers, the common ones are plate and box potentiometers [1]
- In the early 1840s, the method of measuring electromotive force was already known, but at that time it was only based on the assumption that the electromotive force is constant. In addition, most of the measurements at that time were using Galvani cells, which were seriously affected by polarization. It is difficult to get consistent results. In 1860 Clark invented the zinc-mercury standard battery. The voltage of this battery is 1.435v at 15 ° C, and its temperature coefficient is about 0.008v for every 1 ° C increase in temperature. Batteries are a considerable improvement. Soon Clark published details of the device used with this new standard battery and named it "electronic potentiometer", as shown in the figure to the right.
- Clark potential difference meter schematic [4]
- French scientist JSHeari Pellat overcomes the shortcoming that the balance current still flows through the standard battery branch. Figure 7 is the potentiometer circuit that he designed. Instead of placing his standard battery on a separate branch, Pellat was connected in series with the ammeter and connected to a selection switch. Using this switch standard battery can be removed from the circuit and replaced with unknown voltage. The current through the straight sliding wire is first adjusted by the rheostat R to balance a Clark standard battery at 1 000 divisions, so that it can be read directly in thousands of divisions of the standard battery when balancing.
- Schematic diagram of Pellat potential difference meter [4]
- Around 1889, German scientist Feussner designed a potentiometer using a high resistance accurate to 0.1%, which was an admirable figure at that time, as shown in Figure 8. In this device, a sliding wire was used instead, and a scaled manganese-copper resistor was used.
- Schematic diagram of Feussner potential difference meter [4]
- In 1893, British scientists produced the first commercial potentiometer. The overall size of the potentiometer was reduced to about 1 m. The operation of the instrument was greatly reduced due to the selection switch and n pairs of contacts. The circuit of this instrument is shown in Figure 9. They divided the resistance wire of the potentiometer into 15 parts, wound 14 parts into a spiral, and the remaining part was used as the slide wire itself. That helix was divided into 14 parts, and each part matched the slide wire resistance very accurately. In this way, errors caused by the non-uniformity of the wire and errors due to the abrasion effect of the sliding contact on it are largely reduced. Two current adjusting resistors are connected in series in the potentiometer circuit. One is used as a coarse adjustment and the other is used as a fine adjustment. Based on this, the standardized balance can be completed quickly and accurately.
- Schematic diagram of the first commercial potential difference meter [4]