An important aspect of the difference between industrial instruments and laboratory instruments is that they have to consider the harsh conditions of the production site and have a strong ability to resist various interferences. Therefore, when designing and manufacturing this kind of digital instrument, it is necessary to investigate the environmental conditions of the digital instrument use site and formulate corresponding anti-interference measures to ensure that the digital instrument has good environmental adaptability. The scale transformation must be considered so that the unit of the instrument display value is unified with the original physical quantity to be measured. With the increasing degree of automation in modern production, instruments are required to continuously measure a variety of parameters, automatically alarm (overrun, fault), and automatically print records. At the same time, in order to realize the comprehensive control and management of the production process, the measured values of the instrument are often sent to the computer for calculation and storage, so as to control the parameters according to the given rules. Therefore, digital meters are required to have digital output and data communication functions.

Digital Meter Signal Sampling and Quantification Digital meters used in industrial automation need to have their own special properties. There are mainly the following aspects: the detection parameters of industrial automation instruments are usually temperature, pressure, flow, liquid level and so on. These physical quantities are non-electrical quantities that change continuously with time. Non-electricity through a variety of transmitters or A/D, D/A into a unified standard electrical signal, a variety of sensor output electrical signals and the measured parameters often present nonlinear characteristics, and the analog-to-digital converter is generally linear. Therefore, when displaying measurement parameters in digital form, non-linear correction needs to be considered to ensure measurement accuracy.

An important aspect of the difference between industrial instruments and laboratory instruments is that they have to consider the harsh conditions of the production site and have a strong ability to resist various interferences. Therefore, when designing and manufacturing this kind of digital instrument, it is necessary to investigate the environmental conditions of the digital instrument use site and formulate corresponding anti-interference measures to ensure that the digital instrument has good environmental adaptability.

It is necessary to consider the scale transformation so that the unit of the instrument display value is unified with the original physical quantity to be measured. With the increasing degree of automation in modern production, instruments are required to continuously measure a variety of parameters, automatically alarm (overrun, fault), and automatically print records. At the same time, in order to realize the control and management of the production process, the measured values of the instrument are often sent to the computer for calculation and storage, so as to control the parameters according to the given rules. Therefore, digital meters are required to have digital output and data communication functions.

Digital Instrument Signal Sampling and Quantization

Digital meter analog signal: amplitude and time continuous. Discrete analog signal: continuous amplitude, discrete time. Digital signal: amplitude and time are discrete. Sampling: The process of sampling an analog signal into a discrete analog signal at fixed intervals. Quantization: The process of converting the amplitude of a discrete analog signal into a digital signal with a set of codes (binary).

According to the sampling theorem, in order for the sampled output signal U * (t) to accurately reproduce the original input analog signal UI (t), for an analog signal with a finite frequency, the sampling period TS needs to meet the following requirements:

Digital Meter Sampling and Retention

After the analog signal is sampled, a series of sampling pulses are obtained. The sampling pulse width τ is generally short. The obtained sampling pulse amplitude should be temporarily held for conversion until the next sampling pulse arrives. Therefore, a hold circuit is required after the sampling circuit.

Digital Meter Quantization and Coding

Uo remains unchanged during tg, when the circuit quantizes and encodes Uo. Quantization: The sample-and-hold signal Uo is divided into integer multiples of small quantization units S as specified. Encoding: The quantized value is represented by a binary code, that is, the output of the ADC. Due to the limited number of digital meters, a K-bit binary code can only represent 2k values, so it can only approach a certain quantization level value. There are two ways to quantify: if you don't advance, you'll retreat, and if you advance, you'll retreat.

Digital meter analog signal: amplitude and time continuous. Discrete analog signal: continuous amplitude, discrete time. Digital signal: amplitude and time are discrete. Sampling: The process of sampling an analog signal into a discrete analog signal at fixed intervals. Quantization: The process of converting the amplitude of a discrete analog signal into a digital signal with a set of codes (binary).

According to the sampling theorem, in order for the sampled output signal U * (t) to accurately reproduce the original input analog signal UI (t), for an analog signal of finite frequency, the sampling period TS must meet the following requirements:

Digital Meter Sampling and Retention

After the analog signal is sampled, a series of sampling pulses are obtained. The sampling pulse width τ is generally short. The obtained sampling pulse amplitude should be temporarily held for conversion until the next sampling pulse arrives. Therefore, the sampling circuit must be followed by a hold circuit.

Digital Meter Quantization and Coding

Uo remains unchanged during tg, when the circuit quantizes and encodes Uo. Quantization: The sample-and-hold signal Uo is divided into integer multiples of the smallest quantization unit S as specified. Encoding: The quantized value is represented by a binary code, that is, the output of the ADC. Due to the limited number of digital meters, a K-bit binary code can only represent 2k values, so it can only approach a certain quantization level value. There are two ways to quantify: if you don't advance, you will retreat, and if you advance, you will retreat.