Digital sensors and digital weighing system

1 digital technology

Information technology, a new revolution in digital or digital technology has arrived. Digital or digital technology, the simplest is to use two numbers with different combinations of 0 and 1, to express and transmit different information. Where 0 and 1, in the performance of the circuit on and off or on and off, which happens to spend a semiconductor switching characteristics. The simulation technology is used to time-varying waveform analog information changes, attempted to use a simple 0 and 1 to express and transfer large amounts of complex information, you must use a large number of 0 and 1 together according to certain rules. Because digital signals are a combination of 0 and 1, the machine radio frequency interference (RFI) and electromagnetic interference (EMI) performance than the continuous change in the timeline and magnitude axis analog signal to be much stronger. Use of digital technology also easy to achieve integration, from the surface tends to reduce the device size and lower power consumption.

2 analog load cells and digital load cell

Sensors, communications, computers are the three pillars of modern information technology. Load cell detection in industrial processes and commercial settlement, as the heart of electronic weighing components and much attention. At present, the mass production and application of all traditional analog load cell, the smaller the output analog signal to produce the largest, weighing the use of the principle of resistance strain sensor, for example, generally the maximum output (30 to 40) mv, so the signal is susceptible to radio frequency interference and electromagnetic interference, cable transmission distance is short, usually less than 10m. The same strain type of digital sensor systems, the output signal of up to 4v, is the analog sensors 100 times. Strong signal wire transmission distance up to 150m, additional power can be more than 600m.

People have been sending analog load cell for a variety of compensation required for the performance and time-consuming and labor-intensive, especially in the sensitivity of temperature compensation for low-cost, zero temperature compensation, nonlinear compensation, lag compensation, creep compensation, and their interaction may exist between the compensation mechanism and remedies. The digital compensation technology has provided a new solution for this approach, because, microprocessor-based digital load cell system with some intelligence, is conducive to circuit design and software design by digital compensation.

In parallel using multiple sensors in a container weighing systems (scales or hopper batching scale), platform scale weighing system or bridge (Truck or railroad scale), the use of digital system can achieve self-calibration. This is because the multi-channel digital sensor systems, there is no impedance matching problems, the user enters the address of each sensor, weighing and sensitivity, you can automatically balance the scales of the corners or edges do not have time and time again repeated adjustments. In the simulation system in parallel connection of multiple sensors, each sensor's characteristics is no longer discernible, and approval is required in the weight applied to each sensor junction box and use the divider to adjust. Since there is interaction adjustment, therefore, requires repeated many times. In digital systems, allows for review as a monomer, respectively, each sensor. In fact, the more accurate digital sensor system with the time scale, only the simulation system 1 / 4.

Digital system can be achieved using self-diagnosis, diagnostic procedures that will continuously check the sensor signal is interrupted, the output is significantly out of range. If problems in the instrument or control panel to automatically display or alarm, the user can use the keys on the panel to find the various sensors to determine the cause of the problem independently and troubleshoot. This intuitive diagnostic and troubleshooting capabilities, the user is obviously an important advantage, and in the analog sensor system is very difficult to achieve low cost. Typical analog sensor system with 16-bit analog-digital conversion, that is 50 000 counts are available, and the number system, each sensor has a resolution of 20 bits, which can count a million. Therefore, a digital sensor with 4 system can provide four million counts of resolution. The advantage of this high resolution, especially for scale aircraft have been known since the weight of major small occasions.

This traditional analog systems is also difficult to achieve.

3 the development of digital weighing system

One of the key figures of the load cell is between analog and digital signal conversion (ie, A / D conversion), it is through sampling, quantization and coding of three steps. Sample is taken every certain time interval a sample signal with the signal sent instead of sending samples analog signals. Quantitative refers to would have been an infinite number of values ​​of the analog signal, expressed as a finite number of discrete values ​​of the process, even if the analog signal in time and amplitude discrete. Clearly, as long as the sampling frequency is equal to or greater than 2 times the highest frequency signal, then the client can receive the signal without distortion from the sample point to restore the original analog signal. Sample signal is an infinite number of values, limited to binary code that can sample the signal, it can be quantified such as the 65536 level to quantify, quantify the value of each series of 16-bit binary code. Digital sensor in two ways. One is the A / D conversion with pre-amplification, filtering and post-class microprocessor chip, the temperature along the third component, etc., placed inside the sensor housing to form a whole.

The sensor output signal is digital, so the weighing instrument in the analog signal processing unit can be removed. Another way is the sensor itself, as usual, but only the A / D conversion, etc. into the vicinity of the junction box (module, also known as modules). The former is called the global model, which is called the separation type.

A double-shear beam sensor modifications, including about 11 electronic components, a total of 30 joints. Into the overall digital sensor, it will include about 60 350 or more electronic components and solder joints. Sensor, the average time to failure (MTBF) is included with the electronic components is inversely proportional to the number and weld points, and thus the overall reliability of digital load cell is clearly declined.

Distributed digital load cell, or rather digital weighing system, with microprocessor-based digital sensor module replaces the normal junction box. Each sensor signal high-speed and high-resolution A / D conversion is done in this module, you can take up to 12 sensors. Data or information is digitized, serial communication interface, weighing controller transmitted to the digital process. This opto-formed numeric data or data link can transmit digital signals and high frequency interference and electromagnetic interference from electrical noise such as any impact.

Obviously, the decentralized approach is more suitable for the original simulation, based on the weighing system, the sensor can not replace the digital weighing system development, system transformation is a shortcut.