When retrofitting equipment, you may incorporate many sensors — temperature sensors to monitor indoor or outdoor temperatures, humidity sensors to determine the amount of moisture present in the air, CO2 sensors to detect carbon dioxide, or current sensors to measure present power levels.
When using current sensors, there are at least four major types to choose from. Learn more about the key features of these critical sensors and how to decide between them below.
A current sensor measures AC and DC current that passes over it. Some sensors only measure either AC current or DC current, while a few can measure a range of frequencies. It relays the monitored current level and transmits this information to a control board, logic board, switch, relay, or other device that will either display the current level to a worker or automatically perform a specific function.
For example, a current sensor may monitor the current level of a piece of equipment while the device is working. If the current drops to a certain level, a warning alarm may sound. If the current goes over the set parameters, a switch may activate to lower the amount of current or perform a cut-off action to prevent component damage.
Many of the most used current sensor types have a setup where a wire carries the current and creates a magnetic field as a sensor element performs the measurement. These are the 4 major current sensor types and their functions:
Hail effect sensors have permeable magnetic cores with attached Hail effect devices. Conductors pass through the core as the produced current becomes concentrated to make the magnetic field. The hail effect devices become energized by the constant current in one plane. The energized Hail device is then exposed to the core's magnetic field to produce a potential differential. The potential differential becomes measured and amplified into process signals.
A current transformer consists of an iron core that has wire wrapped around it. The coil of wire is connected to another winding that has a second wire coil that is magnetically attached to the primary winding. The current passes through the primary winding to create a magnetic field. This magnetic field induces an electrical current in the second winding. A measuring device is used on the electrical current of the second winding as it has a proportional output voltage to the input voltage.
Unlike other sensors, a Rogowski coil does not have a metal core. Instead, it has a copper wire winding that is wrapped around an air core made of rubber or plastic, as it is not magnetic. The coil of wire is wrapped around the tube to the end and then passes through the center of the core to reach the other end of the copper wire. A current conductor creates a magnetic field that induces a voltage between the Rogowski coils that can be measured.
Shunt resistors come in a wide variety of sizes, shapes, and materials such as resistors made of copper alloy or manganin or as an ohm chip. They are attached parallel to a circuit element. A current flows through the resistor as the resistor experiences a voltage drop. This voltage drop is then measured using a voltmeter to calculate the flowing current in the element.
Each sensor will have specific performance specifications that detail where and how it can be used. It will specify the electrical requirements, environmental factors, and physical installation requirements. You can also select current sensors based on their output interface. Here are several considerations for selecting the right current sensor.
Accuracy focuses on how close the reading will be to the current's true value, while precision focuses on how sensitive the sensor is to detect any slight changes. You also want to understand the drift of the sensor, which means how the reading will change due to aging, temperature, humidity, or linearity where the sensor remains stable over a range of different current signals. Understanding these factors can allow you to locate errors in measurements where you may have to recalibrate the sensor or perform some other compensation technique.
Electrical specifications consist of the voltage and current ratings that will be measured. A sensor often has a maximum current rating or isolation requirement for safe operation. The sensor should also talk about how it handles power dissipation when unwanted heat is created from the device that could disrupt sensor readings.
Moisture, heat, and other environmental factors can also have an impact on a current sensor. A current sensor will feature a safe operating range for the most accurate readings as well as deal with the humidity and vibration tolerance levels. You want to understand the environment that the sensor is working in to select the one that can handle the stresses common to that context.
Sensors can feature different outputs, such as analog vs digital output signals based on the application. It also features how it communicates and transmits this information to other connected devices using specific protocols (I2C, SPI, UART, Modbus, and others). You want a sensor that features the right communication protocols as well as being compatible with your existing systems.
Sensors being mounted on applications may have limited space. You want to consider the physical size and form of the sensor so that it does not become damaged when mounted in tight spaces. Mounting options and wiring considerations can differ based on the sensor as it may offer panel mount installation, clamping/bolting, SMD circuit mounting, surface mount technology (SMT) on printed circuit boards, through hole technology (THT) on printed circuit boards, or handheld products.
Keep in mind that the high accuracy and more functions on the current sensor will raise the price. You want to find a balance between affordability and the performance of the sensor to decide on the right one that fits within established budget constraints. Also, consider the long-term costs associated with maintaining, servicing, and calibrating the device.
The right current sensor for your needs will provide you with the desired measurements at any given time, be easy to install and maintain and work best with your budget. Check out the current monitoring equipment available through Veris to compare your options and find the perfect one for your project.