Sensors for Wireless SCADA Systems

Sensors such as pressure transducers enable users to measure data and make more informed decisions. While the gauge was the primary source of data withing systems, sensors and transducers increase the efficiency of reading the data. They have reduced the need for people to drive to well sites, manually read the gauge, and report back the reading.  Further, sensors are paired with wireless telemetry systems, sending the data to the cloud with greater access and reduced installation cost.

There are different categories of the uses of sensors with wireless systems. Industrial businesses are typically looking to: monitor inventory, measure for maintenance, monitor for safety and control.

Inventory management can be done in various ways.  There are different types of liquid and gas storage tanks where monitoring can be beneficial. Fuel storage tanks can keep equipment from going idle by monitoring the level such that the delivery company knows when it is low. This also reduces their need to check on a scheduled basis. Other tanks such as chemical injection storage tanks can use pressure transducers either internally or externally for level monitoring or dosing the liquid into the system. Gas storage tanks typically use differential pressure transducers to measure the difference in pressure from the bottom of the tank to the top.

When systems can cost thousands of dollars to millions, maintenance of the most expensive components can be vital. Many compressor stations both upstream and downstream use pressure transducers to ensure the engines are running at peak performance. If changes in measurement are detected, the system can be shut down for safety reasons and then checked. If a trend of pressure shows increasing or decreasing, it can also be a sign that changes to engine or filters are required.

There are various mechanical and electrical factors that should be considered in selecting a pressure transducer for wireless monitoring systems including product certification. The process connection of the pressure transducer should be properly rated for the applications pressure and the metal should compatible with the liquid or gas without sacrificing the strength to hold the desired pressure. For example, a 20,000 PSI sour gas application would require an F250C Autoclave type fitting with Alloy 718 or 276C to be strong enough and compatible.  Submersible applications should consider all materials in contact with the liquid including the diaphragm of the sensor and the cable.

Electrical outputs can play a role in the successful deployment of sensors. Voltage output pressure transducers allow for system integrators to operate sensors using a low voltage output, low battery power supply, and operate with low current consumption. It minimizes field service for systems with batteries. For applications where the sensor is hard wired over a long distance and power consumption is not a concern, 4-20mA can be used.

Product certifications span both mechanical and electrical properties of sensors.  From a mechanical perspective, the goal is to contain the liquid or  to the intended system. Electrical safety is usually associated with limiting “arcs and sparks,” or being an electrical source for explosion. The regional certification bodies and electric codes will determine the best option for the hazardous area and the zone in which it is installed. The homogenization of certifications has also helped to clarify the ratings for products certified for operation in one area and shipped to another.

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