At present, the research and prevention of environmental electromagnetic pollution have gained increasing attention. The biological effects of electromagnetic fields have also become a significant area within electromagnetic compatibility studies. Among these, the impact of power frequency electromagnetic fields generated by transmission lines on living organisms is one of the most widely studied topics. However, there remains a lack of effective measurement methods for environmental power frequency magnetic fields. To address this need, we have developed a power frequency weak magnetic field measuring instrument based on the 8032 microcontroller. This device can measure magnetic fields at heights ranging from 1 mm to 1000 mm, with an unknown direction. It provides an efficient method for monitoring environmental power frequency magnetic fields.
**Introduction to AD574 Function**
AD574 is a 12-bit successive approximation analog-to-digital converter produced by Analog Devices in the United States. Its key features include: it has an internal reference voltage and clock circuit, allowing it to operate without an external clock; it offers a high conversion rate, completing a 12-bit conversion in 25 μs and an 8-bit conversion in 16 μs; it supports interfaces with both 8-bit and 16-bit microprocessors, featuring a three-state output buffer that allows direct connection to the microcontroller’s data bus without additional interface circuits; and it operates effectively across a wide temperature range, from -55°C to +125°C, maintaining linearity throughout. The pin configuration is illustrated in Figure 4.
**Pin Functions of AD574**
- **AC:** Analog ground
- **DC:** Digital ground
- **CS:** Chip select signal (active low)
- **CE:** Chip enable (active high)
- **R/C:** Read/start signal—high level for reading data, low level for starting conversion
- **12/8:** Data format selection—high level selects 12-bit mode, while low level outputs the first 8 bits followed by 4 zeros and then the last 4 bits
- **A0:** Internal register control input—when 12/8 is grounded, high level enables the upper 8 bits, low level enables the lower 4 bits, and the middle 4 bits are zero
- **STS:** Status output—high level indicates conversion is in progress, low level indicates conversion is complete
**Power Frequency Weak Magnetic Measuring Instrument**
The hardware of the meter consists of a power module, two main boards, and a magnetic field probe. Given that the instrument is designed to measure environmental power frequency magnetic fields, it may be used for extended periods in outdoor environments where access to power is limited. Therefore, we selected a 12V, 4Ah battery as the power source, along with a charging unit that converts the battery’s output voltage into 12V and +5V using a DC/DC converter (input: 5–18V, output: 12V and +5V). One board is the analog board, responsible for filtering, amplifying, sampling, and selecting signals from the probe. The other is the digital board, which handles analog-to-digital conversion, signal processing (including noise reduction and signal restoration), display, and recording maximum values over a fixed time period. The overall block diagram is shown in Figure 1.
**Analog Circuit Structure**
The block diagram of the analog circuit is shown in Figure 2. Vin1, Vin2, and Vin3 represent the three signals output by the probe. Since the magnetic field being measured is relatively weak, the induced voltage signal contains a power frequency component along with significant noise. To extract the useful signal, we use an RLC series resonant circuit to filter the input signal. The filtered signal is then amplified using a 624Me糯笃鰽 D624 amplifier (controlled by the microcontroller via a single-channel switch AD7502). The output from the three-way sample-and-hold circuit is sent to the AD574 analog-to-digital converter on the digital board through a multiplexer (AD7501), controlled by the microcontroller. This process ensures accurate conversion and processing of the measured signal.
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Ningbo Taiye Technology Co., Ltd. , https://www.tysolarpower.com