The use of a simple squarewave modulation signal to calibrate the Flickermeter is a good representation of simple switching events which may occur in an appliance which the Flickermeter would be used to test. However, in practice, the nature of the modulating signal is essentially arbitrary and the Flickermeter must give the required results for whatever signal is produced by the Equipment Under Test (EUT).

Furthermore, it could be argued that an instrument manufacture could put substantial effort into making a Flickermeter which would meet the requirements of this squarewave calibration test at the expense of giving reliable results for other modulation functions.

An alternative is to test the Flickermeter with sinewave modulation. The frequency domain method described above can be used to find the modulation depth. IEC61000-4-15 provides the theoretical response data for sinewave modulations. NPL has carried-out sinewave modulation tests for several customers.

In order to better address this problem, NPL has extended its Flickermeter calibration facility to include calibrations with more complex modulation signals, which provide a more thorough examination of a Flickermeter than basic square and sine wave modulations. A reference Flickermeter has been developed, which complies with the specifications given in IEC61000-4-15, and this is used to provide a comparison measurement with a Flickermeter under test when a complex waveform is applied. For a full description of the NPL Reference Flickermeter and how it is used for flicker calibrations please see use the links below.

The calibration setup is shown in Figure 8, below.

Figure 8 – System for the calibration of Flickermeters under complex modulation conditions

The required complex waveforms are generated using a PC and Digital to Analogue Converter (DAC). The signal is then amplified and simultaneously applied to the Flickermeter under test and an Inductive Voltage Divider (IVD). The divided signal is sampled using an Analogue to Digital Converter (ADC) and processed off-line using the NPL Reference Flickermeter. The reading given by the Flickermeter under test is then compared with that of the NPL Reference Flickermeter. The complex waveforms used in the calibrations can be found in the NPL Flicker Waveform Library.

Further Documents of Interest

• NPL Reference Flickermeter Design
  This gives a general description of the NPL Reference Flickermeter
• Flickermeter Filter Design and Implementation 
  A description of the design and implementation of the filters used in blocks 3 and 4 of the NPL Reference Flickermeter
• NPL Flickermeter Block 5 Classification Routine 
  Details the NPL implementation of the classification required in Block 5 of the IEC 61000-4-15 flickermeter
• Assumptions in the Design of the NPL Reference Flickermeter and Calibration of Commercial Flickermeters 
  Lists the assumptions used to design the NPL Reference Flickermeter and calibration methodology that are not specified in IEC 61000-4-15
• Testing the NPL Reference Flickermeter 
  Describes the testing and verification of the correct operation of the NPL Reference Flickermeter against theoretical predictions

Remote calibration of Flickermeters >>