Author: Wang De Chao
Shanghai Zhenhua Electric Factory produced 500 million menu, its social has a large amount, the reading is accurate, the number of gear is large, and the general needs can be met.
However, when measuring the insulation resistance of certain products and between the transformer windings and the windings, the insulation resistance between the windings and the core, since the maximum amount of the table is only 20mΩ ("× 10K" gear), it seems to be strong.
to this end. The author applies a "Ga Ziguo" to the 500-type meter (ie "× 1M") block, enabling the resistance gear range of the original table to be 100 times, the maximum measurement value of 2000mΩ, thereby meeting the need for various insulation resistance.
The principles and methods of modification will be described below.
First, the principle 500-type meter "× 10K" block is shown as shown in the figure (the new "× 1M" refill element) is shown in the figure.
The internal resistance value of a gear meter is equal to the numerical value of the ohmic scale center value multiplied by this magnification. For example, the center scale value of the 500 meter ohm gear is "10", the "× 10k" block is 10x10kΩ = 100kΩ.
Similarly, the internal resistance of "× 1m" block is 10 × 1 MΩ = 10mΩ.
The original "x10k" stop battery (E1) voltage is 15V: and "× 1M" block is 100 times based on the "× 10K" gear, so the voltage of the battery (E2) of "× 1MΩ" block should also be E1 100 times. That is, 15V × 100 = 1500V.
Second, the selection and calculation of the program 1. The scheme is installed "× 1MΩ" gear, on the basis of the original "× 10K" gear, adding the "× 1MΩ" gear scheme to the epidemic E2, R two components, As shown in the dotted frame above. The solution does not destroy the structure of the original meter. Do not increase the gear, and "× 10K" gear is relatively independent of "× 1M". Insert E2, R can be inserted when "× 1M" is required; the E2, R is removed when it is not required, and the 500-type mean form is not affected. It does not affect its integrity as the preferred scheme.
2. E2 and R Calculations as shown in the figure above. 1) Seeking R resistance: The internal resistance of the "× 1m" gear is 10mΩ, which is formed by "× 10k" inner resistance (100kΩ) and R series, so R = 10mΩ-100KΩ = 9.9mΩ.
2) The voltage value of E2 is: "× 1M" gear total voltage is 1500V, the original "× 10K" gear current E1 = 15V, and the total voltage value is E2 and E1 series, so E2 = 1500V-15V = 1485V.
Third, assembly is as shown below. B is a mobile transformer with a three-light receiver, the secondary high voltage winding (with the center tap) voltage is 530V. The electrical pressure outputs a + 1499V voltage after D1, D2, C1, C2, C3, and C4 multiplier rectification. After the D3 was dropped 14V. A 1485V DC voltage is established between A and F. That is, E2 (see above): R is formed by a fixed resistor RT (9.1mΩ) and a tonable resistor RR (1 MΩ). Make its total resistance between 9.1 to 10.1mΩ.
Switch the gear switch to "× 10K" gear position, remove the red catering pen, connect it to the H point; access A into the "+" poles; turn on the 220V power supply, to be adjusted.
Fourth, debug will be red (+), black (-) two tablets short, turn the "zero potentiometer" to the middle position, then adjust the resistance of the RT, and accurate the table needle to the ohm irrigation line "0 "Point, adjust the end. Can be used in use.
5. The production of power transformers cannot be found when the AC 5 light receiving power transformer is found. Power transformers can also be made according to the following method: on the EI core of 26.5 mm × 35 mm, the primary winding contains 1100 turns with φ0.15mm enameled wire, and the secondary winding is covered with φ0.13mm enameled wire by 2655.
Sixth, the euros is not a "10" other types of menu, which can also refer to the method of this example to add a "mega" gear to the multimeter to give the multimeter.
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