New sensing technology set to simplify load current measurement
Measuring the input current of a load provides more information than the
current value alone and has a number of advantages. Load changes could
indicate the onset of a fault condition in a process that might not
immediately be detected by monitoring with other devices such as
temperature or pressure sensors. The current sensor is non-invasive,
relatively easy to install and has no moving parts, so it can be regarded
as a true 'fit-and-forget' device.
Traditionally, current transformers have been used to measure electrical
current, but they tend to be bulky, are tricky to set up and tend to
suffer the usual problems of magnetic core devices - hysteresis,
saturation and non-linearity. A new technology from LEM, however, removes
all of these problems and offers scope for the wider use of current
sensing in process automation, energy management and condition monitoring.
The new PRiME (Planar Rogowski I MEasurement) technology solves the
inherent limitations of existing current transformers by employing a
circuit arrangement first proposed in 1912, which senses current via a
special coil arrangement and has no need of a magnetic circuit. LEM's new
AP ('average' rms output) and APR(true rms output) series current
transducers are the first to be based on PRiME technology. These are
entirely PCB-based (no wound coils) and comprise two separate air-cored
coils constructed on a multi-layer PCB. Several sensors are mounted on a
base PCB, at right-angles to it, and connected in series to form the two
concentric inner and outer loops required for the Rogowski measurement.
Unlike current transformers, PRiME allows the sensing head and signal
converter to be combined in the same package, so the AP and APR
transducer provides a compact solution in a single module with only two
connections. The split-core, DIN rail mounting design, moreover, makes
them very simple to install. PRiME transducers offer a very wide dynamic
range (1,000:1 typically), a large bandwidth (several kHz) and better
accuracy. They are also much lighter than their current transformer
counterparts. Twelve different ratings are offered, from 10A to 400A.