FAQs - Current and Voltage Sensors
Is there a minimum order quantity?
Most models do not have a MOQ but some special models come with a MOQ and this information is mentioned in our quote.
What are the delivery timelines for current and voltage sensors?
Depends on the model type. Some are immediate, some might be delivered in 3 to 5 weeks and there are special models which need more than 12-15 weeks.
Does Globetek provide after sales and service?
Yes, Globetek is equipped with an in-house diagnosis and service lab with qualified technicians to provide after sales application and technical support.
Which parameters must be considered when choosing a transducer?
Take into account all aspects of the application
All aspects of an application must be taken into account for the selection of the transducer and system design, with particular attention to the following:
● Electrical requirements, including power supply requirements, peak measurement, response time, di/dt and dv/dt.
● Mechanical requirements, including aperture size, overall dimensions, mass, materials, mounting and vibration.
● Thermal conditions, including current profile versus time, maximum RMS measurement, thermal resistances and cooling.
● Environmental conditions, including vibration, operating temperature range and proximity of other conductors or magnetic fields.
Identify potentially critical elements
Some applications have a higher level of complexity and combine several potentially critical elements such as:
● electromagnetic interference
● significant common mode voltage transients (dv/dt)
● mechanical disturbances (vibration, shock, etc.)
● special isolation or partial discharge requirements
● compliance with specific standards, etc.
Obviously the best scenario is to perform tests in the specific application environment. If this is not feasible, please provide LEM with a diagram of your installation and a detailed description of the transducer operating conditions (e.g. description of the environmental conditions, graph of the waveforms to be measured, nearby potentially disturbing elements such as inductors, current carrying conductors.
How is “primary nominal” rms current or voltage determined?
Sometimes also called “continuous or rated” current (voltage), it is the maximum permanent thermal current (voltage) that the transducer can carry.
Another definition is: the maximum rms current (voltage) which may flow through the transducer under specific conditions, so that the temperature during continuous operation does not exceed the specified value. This is measured with a 50Hz sinusoidal signal.
What does “measuring range” imply?
The measuring region is limited by the maximum measurable peak value in non-steady state.
● Example for closed loop transducers including those based on fluxgates
The transducer can, in fact, measure much higher current values, provided the duration of this current is very brief and non-repetitive. This is then called the dynamic measuring range which is limited by the peak current. In this case, the transducer operates as a current transformer (CT effect).
The maximum peak current will depend on the load (measuring) resistance, bus bar temperature and transducer’s construction. The dynamic range and the admissible duration times (t1…t3) are not determined and are not indicated in the data sheets because of multiple parameters that can interact.
● For an open loop transducer
The measuring range will be linked to the saturation of magnetic circuit or the limit of the voltage output stage.
What is the function of the measuring, burden or load resistor (RM, RB)?
Voltage sensors and current sensors giving a current output need to have a burden resistor (RB or RM - also called measuring or load resistor) connected to their output in order to obtain the correct measurement.
Closed-loop sensors have an integrated current generator that supplies the output signal. The burden resistor is set to define the best current/ to voltage ratio for your application. Current signals are also much less sensitive to external perturbation, which is important when there is larger distance between the location of the sensor and the control electronics processing its signal.
What are the limits of measuring resistor (RM, RB)?
The measuring resistor has to be within a defined range to allow a safe and optimum operation of the transducer.
● The minimum resistor value is set for thermal protection of the output power stage of the transducer. This can be 0 Ω for some transducer types (the maximum power supply voltage will be determining for the calculation).
● The maximum resistor value is set to allow a defined current / voltage measurement range for the transducer. It corresponds to the resistor which will not lead to the electrical saturation. Connecting a higher resistor than the one specified will reduce the measurement range of the transducer (min. power supply voltage will be determining for the calculation).
In case you need values out of the range specified on the datasheet of the transducer, please contact your technical support. Different values can be computed depending on your application conditions (ambient temperature, power supply voltage tolerances and maximum current/voltage to be measured).