An energy meter measures both Current and Voltage to calculate Power and Energy (see Power & Energy). Sometimes it is sufficient to only measure the current, for example to monitor the on/off state of a piece of equipment, or to monitor for faults.
Common applications are:
- Runtime monitoring – keep track of equipment usage and performance
- Fault detection – monitor for broken light bulbs or unusual load conditions
- Slave control – let the on/off state of one machine control other equipment
- Diagnostics – estimate power usage on known loads
Electrical current can be measured in two ways; using a shunt or measuring the magnetic field.
A shunt is simply a resistor. When current flows through the resistor, a voltage will build up over the resistor as described by Ohms Law ; U=R*I, so the voltage over the resistor is equal to the resistance in Ohms multiplied with the current in Amperes. The voltage is easily measured, and knowing the resistance the current can be calculated.
The shunt can be a very accurate way to measure current, but it also adds some loss in the circuit and depending on where the shunt is inserted, isolation may be required between the metering equipment, the ezeio and the circuit.
When current flows through a conductor, a magnetic field is created around the conductor. If the current is alternating (AC), a CT (Current Transformer – see Power & Energy), can be used to safely monitor the current. The easiest way to measure and monitor AC current with the ezeio is to use a Current Transducer (CT) with a 0-5V DC output. Such transducers are available in sizes from 5A to 800A and for 1/4″ to 3″ diameter cables. Refer to our product pages or contact us for details.
Note that monitoring current in a AC circuit is not sufficient to calculate the actual power or energy – even if the voltage is known. This is due to phase shifts that occur when the load is either inductive or capacitive. In practical installations very few loads are perfectly resistive, so that will cause the current and voltage to get out of phase. To measure power/energy with any accuracy, an energy meter is required that monitors both current and voltage continuously. Please see our page about Power and Energy.
If the current is DC (non-alternating), the magnet field will be static, and a different type of CT (Current Transducer) will be required. This type of CT often uses a Hall Effect sensor and some electronics to create a voltage or current proportional to the current measured.
The ezeio may also be used to monitor the current of water, for example in a river. A suitable sensor is needed, but most mechanical flow sensors work in a similar way, and will output a pulse that corresponds to a certain flow. The inputs on the ezeio controller are ideal to monitor the pulse output from such sensors, and will detect both the frequency and the total count, which can be presented as flow, current or volume.