Traditional retro-fit or add-on remote energy monitoring systems use current transformers to monitor the current flowing in supply cables. These systems are often very easy to install (see photograph below) and are useful for detecting excursions in energy consumption or qualitatively checking that energy saving measures are having an effect.
However the accuracy of these systems is limited by a number of factors:
- The current transformers inherently have a finite accuracy typically +/- 1%
- The majority of these systems assume a fixed supply voltage. However the mains voltage in the UK can vary by up to 10%
- For 3-phase supplies, unless the voltage and power factor of all 3 supply phases is measured, the systems do not measure real power – as changes in power factors and supply voltages are ignored. This alone can result in a 20% – 30% discrepancy between the energy consumption as recorded by the revenue meter and by the remote energy monitoring system. The graph below shows an example of the difference between CT measured and actual energy consumption – actual being the amount recorded by the billing meter.
Some modern energy meters are equipped with an electrical pulse output, in which case these can connect directly to a pulse data logger – such as the Crucible Technologies Meter Logger 100. However the majority of energy meters installed in domestic and commercial premises do not yet have the pulse output feature.
To date, the usual solution for accurate remote energy monitoring has been either to replace the existing energy meter with a pulse output equipped meter or to install a secondary meter – for example the Crucible Technologies EML3Net – with both current and voltage measurement. Both of these solutions require an interruption of supply and need to be fitted by a qualified electrician.
The LED Pulse Sensor from Crucible Technologies coupled with the Meter Logger 100 provides a solution which can be applied to any meter with a pulsed LED output – a little red light which flashes at a rate proportional to the amount of energy being supplied by the meter. Examples of a domestic single phase and commercial 3-phase meter fitted with pulsed LED output are shown below – with the pulsed LED circled in red. Adjacent to the pulsed LED is typically an indication of the pulse frequency e.g “1000 imp/kWH” meaning each flash indicates 1 WH used.
The LED pulse sensor is very easy to attach to the meter and alignment guides ensure that the sensor is correctly placed. Once fitted to the meter (see photo below), it is connected to an input on the Meter Logger 100 using inexpensive two core cable; for example loudspeaker cable. Up to 20m cable can be used which allows the Meter Logger 100 to be conveniently located.
The Meter Logger 100 will now record exactly the same energy consumption as the meter but with the benefit of being able to view energy consumption over the web, download into spreadsheet/database programs or send the data via e-mail to AM&T software e.g. Enmat
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