FOT

Multimeter - maintenance experience F117C and F115C

by:FOT     2020-11-24
Maintenance engineers to 115 c and 117 c multimeter maintenance simple instructions. This kind of high-end multimeter is commonly MCU internal process control, the 117 multimeter internal circuit is simple. Functional integration, three pieces of IC inside, A piece of U1 is the A/D conversion, true RMS measurement, non-contact voltage detection. M430F448 MCU U2 do it shows part of the control and simulation shows that there is a piece of 14 feet, role is CD4069 drive buzzer sound. U1 is doing the measurement, that is to say, by measuring the voltage signal, current signal, after exclusion of partial pressures, and the shunt resistance, partial pressure of shunt, U1 in A/D transformation after analog signals into digital signals to U2, 430 single chip microcomputer, display, here 430 microcontroller is not A/D conversion, but control LCD display, and simulation, synchronous display, and there is the role of the U1 is true RMS measurement, that is to say, this chip internal integration, true RMS conversion IC, ac voltage being measured signal after partial pressure exclusion partial pressure, attenuation to the full range of U1 voltage range, after true RMS of U1 internal transformation, into A dc voltage, after U1 internal A/D converter for A/D conversion analog voltage into digital signal and then send to U2, by U2, 430 single chip microcomputer control shows the result. In summary, the function of control is the U1, because the chip integration is very high. He integrated, true RMS, non-contact voltage, AD transform, the principle is the same, and the measured signal into a voltage signal is measured. After 430, according to the single-chip microcomputer control and simulation shows. Here, U3, integrated block, that the pentagon is power. His role is to put the power supply voltage is 9 v, voltage regulator, step-down to U1 and U2 when the power supply. So U3 that the pentagon's little IC die, the multimeter out of electricity. You on the U1 periphery three capacitance voltage measurement is less than three groups. 2. 4 v to 5 v to 3 v, conditional measure, the voltage is normal or not, whether directly conclude that U1 work, among them, 2. 4 v voltage as voltage U1 and U2's communications, if the 2. 4 v voltage is not normal, to 0 v, or less than 1 v, the multimeter is either not boot, or boot error. With multimeter, will encounter boot error, ERR. 2. 4 v voltage is close to 0 v, there are several reasons for that are either to U3 U1 part break line, either U1 virtual welding or peripheral capacitance breakdown ( Less likely) 。 Or U1 breakdown, integrated block 2. 4 v voltage down. But said that if there are any boot, stroke, or simulation does not display, or display and simulation of sync problem, the problem is appeared in the U2. Article because U2 is 430 single chip microcomputer control simulation and display, U2 external crystals if there is a problem, may lead to drop out of sync, strokes, less, because as long as, generally the screen no problem, most will not throw strokes. Summary is to say, for 115 and 117 series of FLuke multimeter maintenance problems if it is function, a function cannot be used, for example, to exclude peripheral problems, ruled out insurance, partial pressure of exclusion, the reason of the protection device, is the problem of U1, because just said the U1 is measured, and U1 integration is high, the probability of bad also. If it is show that part of the problem, that is, the U2, including U2's periphery, but the peripheral rarely bad, most of the more than 430 peripheral bad crystals, shows part of the article simulation does not display or is out of sync, if crystals is no problem, that is the problem of 430, or is not displayed. But if the multimeter is not electricity, that is, the power part of the problem, the majority is break or U3 broken U3, U3 can't give U1 and U2 power supply. Buzzer this, multimeter buzzer this is to use the 117 115, 4069 drive buzzer, generally if the buzzer itself is no problem, don't desoldering pins. If the buzzer rang not most is broken, 4069. Due to the multimeter didn't drawings, at the time of maintenance, test point is hard to find, so, general maintenance is to rely on experience, as long as the working voltage of U1 don't meet, multimeter can't boot, 2. 4 v, 3 v to 5 v, and power supply from U3 U1 and U2, U3 to fail, the entire instrument can not electricity, so generally master the skill, to this kind of intelligent multimeter, circuit is simplified, the better. But in general if U1 working conditions meet the multimeter can be switched on, but if the function part of the problem, the problem or the U1 integrated piece of the above. I maintenance train of thought is, the function of fault check U1, shows some fault check U2.
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