Current Sensors

More Information about Current Sensors

Hall Effect Current Sensors

Hall effect magnetic sensors can be designed as open-loop or closed-loop systems. In an open-loop system, the primary current path does not include the sensor itself, and the sensor measures the magnetic field created by the current carrying conductor directly. This makes them suitable for high-speed current pulses and DC currents. However, they can be susceptible to errors from external magnetic fields and temperature drift, and hence may not offer the highest accuracy.

On the other hand, closed-loop sensors are designed to provide very high accuracy and fast response. In these sensors, the primary current generates a magnetic field in a magnetic core. A secondary coil on the core produces an opposing current to balance the magnetic field. The sensor measures this secondary current, which is directly proportional to the primary current. These sensors offer high accuracy and high resolution, but can be more complex and costly than open-loop sensors.

Current Transformers

Another type of current sensor is the current transformer. Current transformers sense the current flowing through a primary conductor and transform it into a lower, safe level by creating a secondary, scaled current in a secondary circuit.

Rogowski coils, a type of current transformer, can be used to measure AC currents. They use Faraday's law of electromagnetic induction to produce an output voltage proportional to the rate of change of the current in the primary conductor.

Shunt Resistors

Shunt resistors are another low cost but effective way to sense currents. These very low resistance elements are placed in the current path, and the voltage drop across them is proportional to the current flow. However, they can introduce a power loss and may not be suitable for high voltage or high current applications.

FAQs

What is the current sensing element in a Hall effect current sensor?

The sensing element in a Hall effect current sensor is called a Hall effect sensor or Hall sensor. This device, named after the physicist Edwin Hall who discovered the effect, is a thin piece of conductive material, often a semiconductor, that responds to a magnetic field.

What is a data acquisition system used for when determine measured current?

A data acquisition system (DAS) is a system that collects, converts, and stores measurement information from various sensors. In the context of measuring current, a DAS can be used to collect data from one or more current sensors in real-time, convert the sensor output into a format that a computer can understand, and store this data for later analysis or processing.

 Analog and Digital Control Signals: The Basics

Digital Signals

Digital signals are represented in either a true or false. There is no gray area with digital signals. An example of this might be a light switch. A light switch is either on or off. Another example of this might be a motor that is running or not running. Digital signals can be generated with both AC and DC circuits with varying voltages, currents and resistance. Some practical examples of using digital signals in an industrial environment might be if a pump is running or not running or a whether a valve is open or closed.

Analog Signals

Analog signals convey information in the form of a range. A light switch might be on or off as a digital signal, but a dimmer switch would be an analog signal. It can be on or off, but it can also be somewhere in between. A practical example of using analog signals in an industrial environment would be if there is a need to measure the level of a tank; whether it's full, empty or somewhere in between. Analog signals can take many different forms with some of the more common being a 4 to 20 milliamp signal or a 0 to 5 or 0 to 10 volt signal. 

Communication

Communication in a device can either be sent or received. Whether that data is sent or received depends on the type of information. Is there a need to monitor the status of something? If so, an input needs to be received about that information. Is there a need to control something? If so, an output needs to be sent about what needs to occur. Receiving inputs and setting outputs are both things that can be accomplished by using both digital and analog signal types. Therefore, the signals are referred to as analog outputs (AO), analog inputs (AI), digital inputs (DI) or digital outputs (DO).