Serial (RS-485, RS-422, RS-232)

Serial line connections started being used around 40 years ago, and in the last two decades have slowly started to be replaced by TCP-based connections. Serial connections can support a large number of machines, and if they are set up correctly, are a reliable way of connecting. Nevertheless, they have certain limitations, and converting the serial signals to TCP (see Serial Option 2 below) can sometimes be beneficial for the following reasons:

  1. If a converter is used, then data from the serial line can be accessed by any machine on the network. Serial connections only allow a single master/host.

  2. A TCP connection can more reliable and convenient for handling a diverse set of machines with differing serial parameters.

  3. In certain circumstances, the response of a TCP connection is faster than a serial connection.

  4. On occasions, a serial-to-TCP converter can improve the maintenance and diagnostic capabilities of a faulty serial line (for example, the ability to analyse send and receive packages).

Part A: Select Preferred Connection Method

The serial connection can either be made directly from the serial line to the Ardexa Device (Serial Option 1 below), or it can be converted to TCP using a serial-to-TCP converter or a compatible logger (Serial Option 2 below).

In some cases, a SCADA, PLC, etc. hosts information from one or more serial machine(s) and outputs it via TCP (e.g. Modbus TCP). In this case, those systems are acting as a serial-to-TCP converter, shown in Serial Option 2b below.

Serial Option 1: Direct Connection

A direct serial connection requires a serial line to be set up between all machines being connected, and is wired directly into the Ardexa Device. If the Ardexa Device has multiple serial ports, you can connect several of one type of machine to one serial port, and another type to the second port, etc. (as illustrated in Serial Option 1b).

Different types of machines can be connected on the same serial line, however the serial parameters need to be the same, and the serial addresses need to be unique. For more information on setup parameters, see Part B below.

Serial Option 2: Serial-to-TCP Converted Connections

A serial-to-TCP connection is made by setting up the serial line like normal, but instead of wiring the line directly into the Ardexa Device, it is first connected to a gateway. This gateway can be a serial-to-TCP converter or a compatible logger. Serial Option 2b is only possible if the logger has both interfaces, so you will need to confirm with the manual of your equipment to make sure.

Termination Resistance

For both Serial Options 1 and 2, it is important to understand the significance of the termination resistors.

As can be seen, all the diagrams include termination resistors at the beginning and end of the serial line. It is common knowledge in industry that in order for data to be sent correctly, serial lines require termination resistances either at both ends of the serial line or only on one end (if the machine provides built-in termination, please refer to the manufacturer's recommendations to be sure). There are some intricacies that are important:

  • Termination resistance by definition should match the cable characteristic impedance. Since this is often difficult or not practical to measure, the RS-485 standard prescribes a typical termination resistance of 120Ω at both ends of the serial line. This is sufficient in most cases.

  • Although in small serial lines termination may not be necessary, it is always recommended to use it as it ensures that no reflections large enough to cause data corruption occur.

  • The easiest way to set up the termination resistors is to apply them in parallel to the TxD/RxD (or D+/D-) ports on both ends of the serial line, as shown in the diagrams above.

Part B: Identify Setup Parameters

In order to complete the connection of your machine to the Ardexa Device, several parameters need to be sent to the person implementing the connections. The necessary setup parameters will depend on which communication protocol or method is being used. If this is not known, this can often be found in the machine's datasheet or manual. For simplicity, the protocols have been grouped into two major categories. Please select the appropriate category below:

pageStandard Industrial ProtocolspageProprietary Protocols

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