Nowadays varieties of competitions are becoming increasingly fierce in all kinds of industries. With the development of science and technology as a result higher and advanced requirements have arisen,and the market of weighing scale is no exception. Conventional weighing technologies are no longer sufficient for current market demands.
For common platform scales,they can meet regular weighing requirements and have good performance in general weighing purpose. But on some special occasions,usual weighing functions are inadequate. Examples as following:
a) Steel plant site: Fieldbus is easily damaged,crushed,etc. Some problems may exist in fieldbus joints,and it’s also possible that fieldbus can’t be applied because of the on-site situation.
b) Wholesale market: Due to the large space and varieties of goods,it’s hard to move goods to the designated position for weighing purpose,in consequence platform scale needs to be moved. And it’s inconvenient to move scale,meanwhile bus faults may occur when moving.
c) Occasions with sharp changes of temperature: Due to the long distance of fieldbus,the wire resistance value will vary when accompanying temperature change. Then signal will be influenced,finally leading to inaccurate weighing data of platform scale.
d) On-site with harsh environment: Because of severe interferences and long distance bus,bus signal transmission is easily interfered.
In view of the practical need of weighing technology,customers put forward higher requests for platform scales and weighing indicators. Requirements for data centralization and management,as well as remote monitoring are particularly prominent.
Generally most of weighing indicators are used alone,and close connections between weighing indicators are infrequent. When encountering issues of handling weighing data,the most commonly used way is to connect weighing indicator with the screen via method similar to the current loop,to connect a single weighing indicator with a nearby computer via RS232 interface,or connect multiple weighing indicators with a computer via RS485 interface. However several inconveniences along with this conventional connection will be generated.
1) Wiring is required for the connection between weighing indicator and computer. However it is contradictory for purposes of both wiring concealment and easy maintenance.
2) Different interfaces have their own specific requirements for cable length and load number,and load capacity also needs to be considered.
3) For long distance wiring,signal transmission can be easily interfered by on-site environment,especially in harsh environment with electricity and electromagnetism.
Therefore comparing with conventional wiring mode, wireless transmission has great advantages in the circumstance with long distance,heavy load and harsh environment.
At present,multiple wireless transmission modes are available in weighing industry. Here Radio Frequency(RF),Zigbee,and GSM/GPRS,WIFI/Bluetooth modes will be mainly introduced,which can closely connect weighing indicator,platform scale,data processing servers and screen display together.
* RF Mode
Radio Frequency refers to the electromagnetic frequency that can be radiated into space,frequency ranges from 300KHz~30GHz. RF current is a kind of high-frequency electromagnetic wave with AC-changing. An alternating AC which changes are less than 1000 times per second is called a low-frequency current. On the contrary,AC changes more than 1000 times per second,is called a high-frequency current,and RF is one of the high-frequency current. When electromagnetic wave frequency is less than 100KHz,electromagnetic wave will be absorbed by earth surface,which in turn renders ineffective transmission. But if electromagnetic wave frequency is higher than 100KHz,electromagnetic wave can propagate in the air. In addition,electromagnetic wave can be reflected by the ionosphere at the outer edge of atmosphere,which will greatly contribute to a good transmission capability with long-distance.
The high-frequency electromagnetic wave with the transmission capability of long distance is called RF. RF technology is widely used in the field of wireless communication. Some weighing products adopt RF wireless transmission solution,such as crane scale,wireless large screen,wireless weighing platform,etc. What’s more,RF wireless communication can integrate weighing platform,wireless weighing indicator,computer,wireless large screen into a wireless networking communication,to meet the needs of customers.
The way of implementing wireless transmission for common RF is simple. Paired wireless transmissions are often fulfilled by selecting signal channel and matched frequency. Generally common RF wireless transmission has following features:
1) The transmission distance can be up to 1000km~2000km in open area without interference source of same frequency and large interference nearby. Most of customers’ needs can be primarily satisfied,aside from the situation with dense buildings and poor electromagnetic environment.
2) It’s easy to use through transparent transmission,but the information is also easy to be stolen therefore additional processes of encryption and decryption are necessarily required.
3) Common frequency band can be applied,it’s free of charge. However,since this band is frequently used and the frequency band is narrow,consequently,collision phenomenon is hard to avoid. Moreover,as the drift phenomenon of frequency point is serious,which will result in strong frequency interference and high rate of code error under intensive use.
4) System price is low,and consequent maintenance cost is less as well.
In conclusion,common RF wireless transmission is suitable for conditions within medium distance and places without strong interference. This is a good solution for both cost and performance.
* Zigbee Wireless Transmission
Zigbee is an individual network protocol based on the standard of IEEE802.15.4. And the corresponding technology upon the protocol is a kind of wireless communication technology with short distance and low power consumption. The name originated from bees’ dance. The features are short distance,low complexity,self-organization,low power consumption,less data rate as well as low cost. It mainly suits fields in automatic control and remote control,it can be embedded in various devices. Therefore,Zigbee is a kind of cheap and short distance wireless networking communication technology with low power consumption.
Zigbee adopts spread spectrum communication technology,to convert high and narrow frequency into low and wide frequency,to contribute to achieve optimal capability of anti-noise interference. Zigbee has powerful networking functions. It can define the status of each node in advance,and set up a network or search a network automatically when running. Then data can be transmitted through the nearest network path.
Comparing with common RF wireless transmission mode,Zigbee has below features:
1) Zigbee adopts 2.4G frequency band. Because the frequency is high and it’s penetrability is poor,which result in short distance transmission. But Zigbee features the function of automatic networking,and the obvious benefit is it can search the path automatically to transmit the data to the destination node in the case of intensive use.
2) Automatic network function is easy to use,as well as automatic adjustment can be performed when node changes. Moreover transmission with enctyption function via it’s own protocol can guarantee the data security.
3) Zigbee frequency band is often wider than that common RF uses,which contribute to better anti-collision performance and more stable as well.
4) System cost and follow-up maintenance charge are low.
From above points,it can be concluded that Zigbee wireless transmission is suitable for the environment with intensive nodes and complicated constructions,like a market,a production workshop,a warehouse and so on.
* GSM/GPRS(or 4G) Wireless Transmission
GSM/GPRS can achieve transmission and control with ultra-long distance when they are applied in weighing indicators in places covered by mobile network. GSM wireless transmission is easy to use for weighing indicators,the control of short message transmission is easily achieved. Mobile phone sends message to the weighing indicator which connects GSM/GPRS module with valid SIM card,then weighing indicator analyzes and deals with received message,to determine whether it is a valid command of the preset mobile phone number,and perform corresponding response after message handling is completed. Eventually remote control and monitoring actions are fulfilled.
If multiple weighing indicators need to be used,then networking request is hard to fulfill by GSM wireless transmission,and GPRS(or 4G) wireless transmission is required.
Each weighing indicator is equipped with a GPRS DTU(or 4G DTU) with a valid SIM card,and an accessible online computer as the data center. Connect GPRS DTU with data center through internet,and communication between data center and DTU is available via TCP/UDP protocol. Both sides will return received data packets for bi-direction communication purpose. Data center can communicate with multiple DTUs simultaneously.
Therefore multiple weighing indicators can be monitored and controlled remotely through GPRS DTU.
* WIFI/Bluetooth Wireless Mode
Equipped with wireless transmitting and receiving modules,all the data and information can be exchanged between weighing devices under WIFI network and Bluetooth connection.
Common RF,Zigbee,GSM/GPRS wireless transmissions,WIFI/Bluetooth connections,etc. each has it’s own advantages and disadvantages. They are flexible and mobile solutions for delivering smart communications to industrial weighing systems. Users can choose suitable wireless solutions according to requested environment and cost consideration.