Modbus digital communication compared with the advantages of analog signal transmission
Analog sensor and data acquisition technology while performance is strong, but there are also some risks.Modbus as a kind of digital communication protocol, can solve many of these problems.In three series of blog posts about Modbus first article, we introduce the birth of fieldbus protocol, discuss its advantages, and discusses how it has been applied in visa pull equipment.
What is the Modbus?
Modbus developed by Modicon in 1979, is currently on the market has a long history of one of the fieldbus protocol.Its initial development goal is to create an open protocol;After the strategy success, without a license or proprietary hardware, and a control system can freely, Modbus now become the industry standard agreement and get the most of the programmable logic controller (PLC) the support of the brand.Visa products use based on RS - 232 or RS - 485 protocol Modbus RTU, or the Modbus TCP/IP network based on Ethernet.But the Modbus potential defects, the defects in serial connection (RS - 485) is particularly prominent.If you use multiple suppliers configuration, in the same network using different instruments manufacturer, then may occur some compatibility problems between different brands.
Visa Indigo201 simulation data processing unit
Visa Indigo platformCan be widely used in industrial application of a variety of challenging.The composition of its products include simulation of the data processing unit and the connection can be more HuanXing intelligent probe, the probe can be used to measure such as relative humidity and temperature, dew point temperature, the concentration of carbon dioxide and hydrogen peroxide, and other variables.All measurements and calculation by Indigo compatible probe digitally processing, this sensor can also be used as a stand-alone equipment, without data processing unit.Probe will sends the data to the data processing unit, and data processing unit to be connected to the PLC in analog form.
Analog signal transmission problems
Generally, digital humidity sensor (as in this exampleVisa pull HMP3) there are two sensors: one for measuring temperature (such as PT100 sensor), another is used to measure relative humidity (for exampleVisa pull HUMICAP®The sensor);These sensors have actually measured the change of resistance and capacitance.Probe converts analog signals to digital data, necessary for the temperature and relative humidity is calculated, and the accurate digital data sent to the Indigo201 simulation data processing unit.And data processing unit to convert the signal back to analog form, with the help of analog cable connected to the PLC, the PLC place again converted into digital data for processing and storage.
As expected, in the heart of the data processing unit digital data into analog form, and then in the PLC and other control system will increase the error converted back into digital form.From the point of view of quality and supervision, to ensure the accuracy of the measurement is very important, one way is to use digital communication and reduce the error.This is where Modbus can play a role.
The advantages of the Modbus
withIndigo201Tie-in use probe can be compatible with Modbus RTU digital communication protocol.Because the Modbus use digital communication, so the probe in addition to measure the relative humidity and temperature, can also be used to measure many other parameters, including/frost dew point temperature, absolute humidity, mixing ratio, wet bulb temperature and enthalpy, as well as access to equipment status, serial number and secure Hash function, etc. For more information.Check safety Hash state allows Modbus Master ensures that the sensor was not tampered with and without changing the probe configuration.Multiple probes can also be connected to the same network;In the simulation system, to achieve this requires in PLC system installed in a large number of additional cables and (I/O) module.Modbus also by minimizing between analog and digital conversion to reduce the risk of data error, thus become the ideal choice of the digital data transmission.
The data processing unit is not only an analog to digital converter agreement
Although Indigo compatible probe can be used as a independent measuring instrument, but in order to achieve good availability, usually need to with the local user interface, display and data processing unit of a variety of power options collocation is run, the data processing unit of a part of the model has the advantages of digital communication.Indigo202 data processing unit to provide consistent with the probe of the Modbus RTU, andIndigo500 series data processing unitModbus TCP/IP protocol is used for communication.
Watch the Modbus network conference, 101 for more information!
