There is a wide variety of digital weight control indicators (often referred to simply as digital indicators). These devices receive and process electrical signals output by load cells. These signals can be either analog or digital, with the most common type being an analog voltage ranging from a few millivolts to several tens of millivolts. Regarding circuit principles, the excitation power supply provides operating power to the load cell while simultaneously supplying a reference voltage to the A/D (analog-to-digital) conversion unit; its stability is generally better than 0.1%. The amplification unit typically employs an instrumentation amplifier configuration to receive and amplify the load cell's signal, usually providing a gain of several hundred times. The filtering unit removes electrical noise-whether introduced from external sources or generated internally by the amplifier itself. The A/D conversion unit converts analog signals into digital data, typically utilizing a resolution of 14 bits or higher; modern high-precision indicators often employ technologies such as Sigma-Delta (Σ-Δ) conversion, achieving resolutions of up to 24 bits and conversion rates of 10 to 100 samples per second, with an input signal range generally between -2 mV and +19 mV. The data processing unit is centered around a microprocessor and supported by peripheral chips; under program control, it performs tasks such as data acquisition, calculation, and storage, subsequently sending the processed results to the appropriate interfaces. The display unit presents the weighing value and status using digits, text, or graphics, and can communicate with external devices via interfaces.
To facilitate data exchange and control, weighing indicators are typically equipped with various communication interfaces. RS-232 is one of the most common serial interfaces; it utilizes a three-wire configuration consisting of Transmit (TXD), Receive (RXD), and Ground (GND). Logic levels are defined relative to GND (Logic 1: -3V to -15V; Logic 0: +3V to +15V). It supports a maximum transmission distance of approximately 15 meters and a maximum data rate of about 20 kb/s, making it primarily suitable for point-to-point communication. Modern industrial weighing indicators widely support bus or network interfaces such as RS-485, PROFINET, EtherNet/IP, EtherCAT, and Modbus RTU, as well as IT system data exchange protocols like OPC UA and JSON REST API, enabling integration with external devices-such as PLCs and computers-and remote configuration.
Under program control, the data processing unit (microprocessor) not only performs basic data acquisition, calculation, and storage but also executes functions such as automatic zero-setting, zero tracking, digital filtering, non-linearity correction, peak hold, and setpoint control. Software can simulate weighing characteristics-such as vibration and empty-scale fluctuations-to optimize performance. In accordance with the national standard GB/T 7724-2023 "Electronic Weighing Instruments," weighing indicators must possess interference immunity; when subjected to disturbances such as electrostatic discharge, voltage dips, or surges, the variation in the indicated value must not exceed one scale interval, or the instrument must be capable of detecting significant errors and responding accordingly.