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Electrical Power and Energy Measurements
Power is defined as P = iv, where i and v are the instantaneous values of the current and voltage. For constant DC, power is simply the product of the voltage and the current. For AC power it is not quite so simple. Most watt transducers measure the instantneous power averaged over some time interval to obtain real average power.
Because watt transducers measure the rate at which work is being done they are an invaluable feedback device for discreet control of a process. Examples include cutting, grinding, heating, welding, pumping and mixing.
Watt transducers have one or more elements. Elements are also referred to as multipliers.
Remember Blondel's Theorem:
For any (n) wire sysem, (n-1) wattmeters or elements are required to measure total power. For more information please refer to the technical paper in our Tech Library entitled "Selecting and Using Transducers for the Measurement of Electric Power, Voltage and Current".
Almost the entire output of the electric power industry in the United States is generated and distributed as polyphase power at 60Hz. In a three phase system the three voltages are mutually out of phase by 120°. A balanced load will draw equally from the three phases: however, when one of the voltages is instantaneously zero the phase relationship shows that the other two must be at half amplitude. At no time does the instantaneous power drawn by the load reach zero. In fact the total instantaneous power drawn by the balanced load is constant. This is a big advantage for rotating machinery because it maintains a more constant torque than if a single phase motor were used.
Utility power is generally referred to as "Y" or "Wye" or a three-phase, four wire connected system. To determine the total power each of the three branches must be monitored. The total power delivered by the source load will be the simple sum of the readings of the watt meters on each branch,
OSI watt transducers for monitoring a wye-connected load have three individual multipliers (elements) contained in the transducer housing.
Polyphase watt transducers manufactured by Ohio Semitronics, Inc. are rated for voltage in two ways:
Three phase, three wire two element watt transducers are rated for line to line voltage.
Three phase, four wire three element watt transducers are rated for line to neutral voltage.
Measuring power accurately on non-linear loads can present problems. Examples of non-linear loads include UPS systems, electronic power supplies, lighting ballasts, battery chargers, variable frequency motor drives, phase angle-fired SCR controllers, zero crossing SCR controllers and pulse wave modulated controllers. While these non-linear loads can create high neutral currents, voltage distortion, heat and reduction of system power factor it is possible to measure power accurately if the correct power transducer is selected. You should consult with your OSI Technical Sales Specialist when considering the purchase of a watt tranducer which will be applied on a non-linear load.
Typical Watt, Watt-hour, VAR and VAR-hour transducers manufactured by OSI include the following models:
Accurate regardless of voltage, current, power factor or load. Output is proportional to true power delivered to the load. Provides bi-directional operation.
Typical Applications
SCR controls, chopped waveforms or where harmonic components exist. Also available in 400Hz models (specify PC4 prefix when ordering)
Input Range
Std.Outputs
Accuracy
0-600Vac
See spec sheet for individual model numbers and complete product specifications including current input range limits.
Analog output for instantaneous watts and relay closure or pulse output for watthour consumption. Maintains accuracy with chopped or distorted waveforms through the use of a real-time multiplier.
Typical Applications
Building energy management systems, process control, electric motor power consumption, welding/soldering process monitoring and battery charger monitoring.
Input Range
Std.Outputs
Accuracy
0-600Vac
See spec sheet for individual model numbers and complete product specifications including current input range limits.
UL Listed. Accurate regardless of variations in voltage, current, power factor or load. Available in 1,2, 2.5 or 3 element configurations. Bi-directional operation.
Typical Applications
Equipment monitoring in process control, energy management systems and a variety of electrical sub-metering applications.
Input Range
Std.Outputs
Accuracy
0-600Vac
See spec sheet for individual model numbers and complete product specifications including current input range limits.
Accurate regardless of variations in voltage, current, power factor or load. Available in 1,2, 2.5 or 3 element configurations. Bi-directional operation.
Typical Applications
Widely used in hydroelectric generator output measurements, end-of-line appliance testing for energy consumption and cogeneration systems.
Input Range
Std.Outputs
Accuracy
0-600Vac
See spec sheet for individual model numbers and complete product specifications including current input range limits.
Accurate regardless of variations in voltage, current, power factor or load. Available in 1,2, 2.5 or 3 element configurations. Bi-directional operation. Provides Leading/Lagging VAR indication.
Typical Applications
Widely used in hydroelectric generator output measurements, end-of-line appliance testing for energy consumption and cogeneration systems.
Input Range
Std.Outputs
Accuracy
0-600Vac
See spec sheet for individual model numbers and complete product specifications including current input range limits.
Accurate regardless of variations in voltage, current, power factor or load. Available in 1,2, or 3 element configurations. Some models provide bi-directional operation.
DIN rail mount and CE/CSA approvals.
Typical Applications
Process control, SCADA,submetering applications where the power being measured is a sinusoidal waveform. Not recommended for variable frequency drive applications or PWM drives.
Input Range
Std.Outputs
Accuracy
0-600Vac
See spec sheet for individual model numbers and complete product specifications including current input range limits.
Available in 1,2, or 3 element configurations. Accuracy maintained over a wide temperature range.
Typical Applications
Process control, energy management and submetering applications where the power being measured is a sinusoidal waveform. Not recommended for variable frequency drive applications or PWM drives.
Input Range
Std.Outputs
Accuracy
0-600Vac
See spec sheet for individual model numbers and complete product specifications including current input range limits.
Available in 1,2, or 3 element configurations. Some models provide bidirectional outputs. Compact DIN rail package with both CE and CSA approvals.
Typical Applications
Process control, energy management and submetering applications where the power being measured is a sinusoidal waveform. Not recommended for variable frequency drive applications or PWM drives.
Input Range
Std.Outputs
Accuracy
0-600Vac
See spec sheet for individual model numbers and complete product specifications including current input range limits.
The DSP is a 3 phase, 3 element multifunction digital transducer with outputs for voltage, current and power via serial communication. All measurements are true RMS values. Data is available via a serial RS-422 port using a simple ASCI protocol. A PC data system and LabView™ Driver are available for programming and reading values from the DSP.
Typical Applications
Widely used in test and measurement applications where precise electrical measurements are required and digital communication is preferred for data logging during performance testing.
Input Range
Std.Outputs
Accuracy
0-600Vac
See spec sheet for individual model numbers and complete product specifications including current input range limits.
Serial:
L-N RMS volts, 3 phases
L-L RMS volts, 3 phases
Per Phase Current, 3 phases
Per Phase Power
Total Power
Frequency
(measured at L1-N)
Power Factor
An A/D converter for analog output is available as an option.
The GH watt-watthour transducer provides an analog output proportional to time-averaged instantaneous true power and a relay closure or TTL pulse output calibrated in watthours of energy consumed by the load. Accuracy is ±0.2% of reading. Models are available in 1, 2, 2.5 and 3 element configuration. Bidirectional watt and watthour. See spec sheet for individual model numbers and complete product specifications including current input range limits.
Typical Applications
The Model GH is used extensively in utility submetering, generation control and appliance testing to verify compliance with either advertised or federal standards.
The VGH VAR/VARhour transducer provides an anlog output proportional to time-averaged instantaneous reactive power and a relay closure or TTL pulse output calibrated in VARhours for reactive energy. Accuracy is ±0.2% of reading. Models are available in 1, 2, 2.5 and 3 element configuration. VAR and VARhour outputs are available. See spec sheet for individual model numbers and complete product specifications including current input range limits.
Typical Applications
The Model VGH is used extensively in utility submetering, generation control and appliance testing to verify compliance with either advertised or federal standards.
The MT transducer provides an output signal which is directly proportional to the instantaneous product of the two input signals. Each input and the output are isolated from one another up to 1000 volts DC. The MT series should be used where two process quantities must be multiplied to obtain a useful quantity. See spec sheet for individual model numbers and complete product specifications including current input range limits.
Typical Applications
An example would be a shunt output multiplied with the system voltage to obtain DC power delivered to a load. The multiplier provides full four quandrant operation so signals that may change polarity during operation can be accurately multiplied.
The PC 20 provides three seprate outputs proportional to true power, VA and power factor in single or polyphase power systems. True power and VA measurement for sinusoidal and distorted wave forms.
Typical Applications
Electrical equipment monitoring to determine and/or maintain efficiency or consistent product quality.
For use with SCR controlled, chopped or otherwise distorted waveforms.
Input Range
Std.Outputs
Accuracy
0-600Vac
See spec sheet for individual model numbers and complete product specifications including current input range limits.
