与模拟信号传输相比，数字modbus通信的好处

Although analog probes and data collection technology have a lot to offer, they also present several risks. Modbus is a digital communication protocol that overcomes many of these issues. In this first blog post in a series of three about Modbus, we introduce this established fieldbus protocol, discuss its benefits, and explore how it is implemented in Vaisala devices.

What is Modbus?
Modbus was developed by Modicon in 1979 and is one of the oldest fieldbus protocols available. The initial intention was to create an open protocol; thanks to the success of this strategy Modbus is now seen as an industry-standard protocol and supported by most programmable logic controller (PLC) brands because no licenses or proprietary hardware are needed and it’s free to implement a control system. Vaisala products use either Modbus RTU, which is built on the RS-232 or RS-485 protocol or Modbus TCP/IP, which uses an Ethernet network. One potential downside of Modbus especially in serial line communication (RS-485) is that if you have a multi-vendor configuration that uses instruments from different manufacturers in the same network, there may be some compatibility issues between the different brands.

Vaisala Indigo201模拟发射器
TheVaisala Indigo平台is used extensively in a wide range of challenging industrial applications. The product consists of an analog data transmitter attached to an intelligent, interchangeable probe that measures variables such as relative humidity and temperature, dew point temperature, carbon dioxide or hydrogen peroxide concentration. All measurements and calculations are performed digitally by the Indigo compatible probe, which is also capable of operating as a standalone unit without a transmitter. The probe passes the data on to the transmitter, which then sends it to a PLC in analog form.

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模拟信号传输的问题
Typically, a digital humidity probe, in this case, aVaisalaHMP3，有两个传感器 - 一个测量温度的传感器，例如PT100传感器，一个用于相对湿度，例如Vaisala humicap^®传感器;实际上，这些传感器实际上分别测量了电容和电容的变化。探针将模拟信号转换为数字数据，对温度和相对湿度进行必要的计算，并将精确的数字数据发送到Indigo201模拟发射机。然后，发射器将该信号转换回模拟形式，以通过模拟电缆传输到PLC，在此再次将其转换为数字数据以进行处理和存储。

正如预期的那样，将数字数据转换为数据发送器中的模拟形式，然后在PLC或其他控制系统中返回数字将引入其他错误源。从质量和监管的角度来看，确保准确的测量很重要，最小化错误的一种方法是使用数字通信。这是Modbus进来的地方。

Modbus的优势
可以与Indigo201are also compatible with the Modbus RTU digital communication protocol. Because Modbus uses digital communication, in addition to relative humidity and temperature the probe can also be used to measure many other parameters including dew point/frost point temperature, absolute humidity, mixing ratio, wet-bulb temperature, and enthalpy, as well as additional information such as device status, serial number, and security hash. Allowing the Modbus master to check the security hash status allows you to ensure that the sensor hasn’t been tampered with and that the probe configuration has not been altered. It’s also possible to connect multiple probes to the same network; with an analog system, this would require a substantial amount of additional cabling and (I/O) modules to be installed in the PLC system. Modbus also reduces the risk of data errors by minimizing conversions between analog and digital, making it a great option for digital data transmission.

发射器不仅是数字协议转换器的类似物
尽管Indigo兼容探针可以用作独立测量仪器，但通常可以与提供本地用户界面，显示，不同的电源选项以及其中一些具有数字通信优势的发射器一起实现最佳可用性。Indigo202发射器提供与探针相同的Modbus RTU和Indigo500 series transmitterscommunicate with Modbus TCP/IP-protocol.

To learn more, watch theModbus 101网络研讨会或者或者联系我们.