Construction and Use of Standard Battery |
Posted: July 12, 2019 |
Standard battery construction The structure of the saturated standard battery and the unsaturated standard battery are basically the same, the positive electrode is mercury (Hg), and the negative electrode is cadmium amalgam (Hg Cd). The difference between the two is that the saturated battery cadmium sulfate (CdSO4) solution is saturated and has an appropriate amount. Cadmium sulfate crystals (see photo). The internal resistance of a saturated standard battery is about 700 Ω, and the internal resistance gradually increases with time. If current is output from a standard battery, the terminal voltage drops. Therefore, the use of a standard battery as a standard circuit must have a very high impedance. However, instantaneous output current from a standard battery generally does not permanently damage the standard battery, but it takes time to revert to the original state. If a good standard battery is shorted for 1 s, it takes about 6 hours to recover. A saturated standard battery with excellent texture has a long-term stable electromotive force. However, it can be affected by mechanical shock, thermal shock or temperature changes. Usually, the effect of mechanical shock is less than the effect of temperature changes, and can be recovered in hours or even minutes. As long as the battery is in good condition, the standard battery after shipment can be restored to its original state within a few days. Of course, severe vibrations should still be avoided. The temperature change has a great influence on the electromotive force of the standard battery. There are two forms of this effect: one is that the electromotive force changes with temperature, and the other is the hysteresis. Standard battery use Standard batteries are not allowed to be shaken, placed sideways, and violent vibration or inversion, otherwise it will cause irreversible changes or even damage. The standard battery cannot be used as a primary battery for outputting electric power. The current through the standard battery during use should generally not exceed 1 microamperes. Excessive current will cause an irreversible change in the electromotive force. The temperature coefficient of the electromotive force of a saturated standard battery is large, about 4×10-5/open, and it should be generally ensured that the temperature at the time of inspection and the use is consistent. If there is a difference between the two, you need to use the interpolation formula to correct. In precision measurement, in order to ensure the stability of the standard battery electromotive force value, the standard battery needs to be placed in the oil tank with automatic temperature control. The temperature range of the oil sump is about ±0.01, and the high quality oil sump can reach ±0.001. Since the 1970s, air thermostatic chambers controlled by electronic devices have been developed, which have high temperature stability and can be made portable, and thus are widely used. Standard battery usage precautions From the principle, structure and characteristics of the standard battery, it is necessary to pay attention to the following five points when using the standard battery. 1 Standard battery does not allow tilting, and it is not allowed to shake and invert. Otherwise, the chemical substances in the glass tube will be mixed into one, which will affect the electromotive force value and stability, and even cannot be used. The standard battery after transportation must be allowed to stand for a sufficient period of time before being used; any battery that has been reversed can be used after passing the test. 2 Can not be overloaded. Standard batteries generally only allow currents of less than 1μA, otherwise the electromotive force will be unstable due to polarization; the current flowing through the standard battery should not exceed the allowable value; do not touch the two terminals at the same time by hand to prevent the human body from short-circuiting the two poles; Never use a voltmeter or multimeter to measure the electromotive force of a standard battery, because the internal resistance of this meter is not large enough, the battery discharge current will be too large. 3 The temperature and humidity used and stored must comply with the regulations. Temperature fluctuations should be small to prevent errors due to hysteresis. The temperature gradient should be small to prevent the temperature of the two electrodes from being inconsistent. If the temperature difference between the two electrodes is 0.1 °C, there will be an electromotive force deviation of about 30 pV. Therefore, there should be no cold source or heat source near the battery. It must be kept at a constant temperature for a period of time before moving to a new temperature. 4 Should not be exposed to the sun or direct light. Because the standard battery depolarizer, mercuric sulfate, is a light-sensitive substance that deteriorates when exposed to light, which causes both polarization and hysteresis to become severe. 5 The polarity of the standard battery cannot be reversed. Since the terminal voltage of the Zener diode is almost independent of the fluctuation of the reverse current in a small range, it can also be used as an electromotive force standard in an instrument instead of a standard battery. Visit my website to see more electronic components: http://www.icchipword.com/
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