MLT-1000 User Manual
Overview
Excel Technology Co
Page
3
1
Overview
The Excel Technology Co MLT-1000 is a portable field service device for in-pavement loop analysis. It is
capable of measuring loop inductance, DC series resistance, Q performance factor and loop resonant
frequency for a group of up to eight in-pavement loops. It can also detect open and short circuit conditions.
The MLT-1000 is based on Excel Technology Co’s LTM-100 basic loop tester. The MLT-1000 includes
additional switching circuitry that allows up to eight in pavement loops to be measured simultaneously. The
device is also capable of measuring loops while traffic is flowing by filtering out vehicles from the
measurements. The device is powered and controlled by accompanying PC software via a USB connection.
The software allows the user to easily log and save loop data and store it along with relevant site
information.
1.1
Terminology
In-pavement induction loops can be characterised by their inductance and DC resistance. The overall
sensitivity of the loop is measured by a performance factor Q.
Inductance is a property of a conductor that opposes a change in current. Inductance is measured in
Henries (H), but is commonly displayed in Microhenries (µH). Inductance depends on the size, number of
turns, configuration of the loop, length of the feeder cable and environmental factors (e.g. steel
reinforcement in road, temperature).
DC series resistance is a property of a conductor that opposes current flow. The resistance of a wire
depends on its material, cross-sectional area and length. Therefore, an inductive loop using thin cable with
a large number of turns and a long feeder cable is likely to have a high DC series resistance.
The Q performance factor of a loop is effectively a relationship between the inductance of a loop and the
resistance/impedance of the feeder cable. The Q-factor is calculated as:
𝑄 =
2×𝜋×𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦×𝐼𝑛𝑑𝑢𝑐𝑡𝑎𝑛𝑐𝑒
𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒
The higher the Q-factor, the more sensitive the loop is. Therefore, if the resistance of the loop and feeder
cable is large, then the inductance must be large to maintain high sensitivity. For vehicle detection, the Q-
factor of a loop should be in the range below for the corresponding frequency ranges:
Q-factor = 5 to 50 for Frequency < 60 kHz
Q-factor = 3 to 50 for Frequency ≥ 60 kHz
For reliable vehicle classification or identification, the Q-factor should be in the range 15 to 50.
