Replacement techniques for integrated digital multimeter Blocks

Currently, almost all digital multimeter use dedicated integrated circuits for A/D conversion. Table 1 lists some common number table A/D chip configurations.

I. Replacement of the mode/number Converter

Currently, almost all digital multimeter use dedicated integrated circuits for A/D conversion. Table 1 lists some common number table A/D chip configurations.

Icl7106, icl7126, and icl7136 belong to the icl7106 series and can drive 3 1/2 LCD display. They are the most commonly used chips in hand-held digital tables.

Icl7126 is an improved version of icl7106. Its power consumption is only 7106 of 1/18, and icl7136 is an improved version of 7126. The three indicators have the same accuracy, working principle and pin arrangement, and can be directly exchanged with each other. Domestic chips can be directly replaced with ch7106 and dg7126.

The difference between icl7116 and the former is that 7116 adds the data lock function. The icl7106 series chip cannot be replaced with icl7116 directly. You can change it a little before replacement. The specific modification method is as follows: connect the 35-pin 7106 chip with the 32-pin, and disconnect the 35-pin from the circuit.

Icl7l07 and icl7107 belong to the same icl7107 series and are a 3 1/2-bit dual-integral A/D converter designed to drive LED display. Here, icl7l37 is an improved version of icl7107. Both of them work in the same principle and pin arrangement and can be directly replaced. The same type of products that can be replaced in China include dg7107

.

Icl7129acpl is a cost-effective 4-1/2-bit LCD single-chip A/D converter. It is widely used to form four 1/2-bit digital multimeter, such as dt930f +, dt930fg, dt980, dt1000, and dm6017. Only chips of the same type can be used for replacement. A few days ago, there were many inferior 7129 chips on the market, which were mainly characterized by poor linear characteristics and low accuracy than genuine ones. The reason is that this type of inferior 7129 chip has a linear difference in the internal op amp, and the output is saturated. The remedy after replacement is to adjust the integral resistance or integral capacitance value of 7129, make it work in a linear state.

ICL7135 is a 4 1/2 LED display single-chip A/D converter. Domestic replacement models can be 5g7135 and dg7135.

The tscl4433 is a 3 1/2 led dual-integral a/I) converter. In China, chips such as mcl4433, 5g14433, and chl4433 can be exchanged with each other.

Ap25, tsc815, tsc820, tsc818a, tsc818d, and other A/D chips are mostly high-performance analog-to-digital converters developed in early 1990s S. Currently, no corresponding model products are available in China. Only chips of the same model can be used for replacement.

Ii. Replacement of other Integrated Circuits

In addition to the/D chip, the digital multimeter is generally equipped with other analog and digital integrated circuits, and most of them are general-purpose products. Here we only introduce the replacement of precision reference voltage regulator integrated circuit essential for High-accuracy digital multimeter.

Currently, most of the reference voltage sources of the digital multimeter have been serialized. The output reference voltage is divided into 1.2 V, 2.5 V, and V. In addition to the output reference value, the most important technical indicator is the voltage temperature coefficient, that is, the output voltage variation caused by the unit temperature change, also known as temperature drift, in ppm/℃. It directly affects the long-term stability of the digital multimeter and the level of accuracy that can be achieved. Table 2 lists common reference voltage source parameters and Replacement Models of the digital multimeter.

3. Replacement of the monitor

Currently, most digital multimeter uses a digital diode (LED) and a liquid chip (LCD) as the display, most of which are used by desktop instruments, while LCD is often used for portable digital tables.

The replacement of a digital diode generally has no special requirements. You only need to identify whether the public pole (Common Yin or common Yang) is consistent.

Liquid Crystal is a kind of crystalline material between the solid state and the liquid state. It is a common two types of Liquid Crystal Display reflective type and columnar type. Low voltage and low power consumption, easy to be driven by CMOS circuit, handheld digital multimeter generally uses it as a display.

Two LCD Driver methods are available: one is static drive. Each pen segment of the LCD corresponds to one drive end, And the LCD only sets one BP end of the public back electrode, the display part of each section is synchronized at the same time. Therefore, this method has a large number of LCD pins. For example, the LCD used with the lcl7106 series A/D chip is a static display, which displays 3 1/2-bit actual pins.

The number is 27.

Another method is dynamic driving. In this way, the LCD has multiple back electrodes, and each segment is divided into several groups. The pen segments of each group emit light in turn in a certain sequence. This LCD feature greatly reduces the number of pins. The icl7129 A/D Converter uses a 1/3-offset dynamic drive LCD, which displays 4 1/2-bit numbers and the actual number of pins required is only 15.

When changing the LCD, the driver mode must be differentiated, and the display digits must also be consistent. Only when both of them meet the requirements can they be replaced directly.