For safe operating conditions underground, the list of parameters to monitor is ever increasing. Airflow, pressure, temperature, air quality – all this needs to be monitored and more. Keeping track of all this data can be overwhelming. A well-designed communication system can help manage and monitor this data for better automation, and ultimately safer working conditions.
Analog and Digital Signals
Many measurement devices, such as piezoresistive pressure sensors, output analog signals. Analog signals are continuous signals which vary over time. Typically, this refers to electrical signals. When measuring something such as the velocity of air in a drift, the measured value will most likely be an analog signal. For instance, our FlowTRAX Ultrasonic Senor outputs an analog signal in a range of 4mA to 20 mA. What this means is that the device is outputting a time-varying analog signal – in this case current – which will change with respect to the velocity of the airflow. Faster airflow will produce a different current value than slower airflow. How can this current value be read to produce a value for airflow, and how can this value be accessible to a network of devices? This value must be converted from it’s analog signal to a digital signal.
The conversion is done by an analog-to-digital converter, such as our I/O TRAX device. The methods for converting an analog signal to a digital signal can be complex. One common method of performing this conversion is to use the analog signal to charge up a capacitor, and measure the discharge time over a resistor and calibrating this value to provide a digital reading. The I/O TRAX takes in an analog 4mA to 20 mA signal, which is what is commonly output by many ventilation monitoring devices, and converts this to a digital Modbus RTU signal.
Modbus is a communications protocol used for PLC. Modbus is easy to use, open source, and useful for large communication networks with many devices. Thus, this became the go-to protocol for industrial applications.
Modbus RTU is the most common of the Modbus family. This is typically used for serial communication and is works on the master/slave architecture. Modbus RTU allows for simpler programs of reduced size when compared to other typical communication protocols.
Modbus TCP uses the TCP/IP protocol. This is most commonly used for ethernet attachments of PLCs, I/O modules, and gateways to field buses or I/O networks. Modbus TPC is essentially a Modbus RTU message which is transmitted with a TCP wrapper and sent over a network rather than a serial line. This allows for easier access to the information and allows for Modbus communications to be managed remotely over a network. This means that your information can be better organized and more easily accessible.
Converting Modbus RTU to Modbus TCP
Converting Modbus RTU to Modbus TCP can be done by simply employing a gateway device such as our CommTRAX Protocol Converter. This device accepts Modbus RTU inputs in the RS232/RS485 Master port, and this can then be output to Modbus TCP via an ethernet connection. This can then be sent to a network switch to be used for HMI, SCADA, or to be accessed via web browser for monitoring purposes.
Supervisory control and data acquisition (SCADA).
SCADA is a control system used for monitoring and controlling production processes for a wide range of industrial applications. SCADA systems use computers to communicate with networks through a graphical user interface. SCADA systems also use PLCs and PID controllers to interface with process plants and machinery. SCADA systems are excellent for monitoring sensors and automating processes.
Accutron offers an all-in-one communications system, able to accept signals directly from sensors and convert them for digital use. This means that analog sensors can be converted simply and efficiently and accessed remotely or used by SCADA systems.