4
Instructions for Measuring Loop Characteristics
Step 1
Connect the two loop feeder leads using the alligator clips. There is no polarity however the clips
should be attached in a manner which does not short circuit the connectors that would cause
malfunction and or false readings.
Step 2
Switch on the unit via the ON/OFF switch – the unit will automatically switch off after a preset period
of no activity. The unit will hold on and display data while connected to a loop.
Step 3
If using the LTM 1000 at night press the momentary button to enable the backlight. Excessive use of
the backlight will decrease the battery life.
Step 4
The screen display is self explanatory
Frequency:
Is the resonant frequency of the loop (Typically 15-140Khz).
Inductance:
Is the inductance value of the loop (Typically 40-700 MicroHenries)
Resistance:
Is the DC resistance of the loop (Typically 1-3ohms)
‘Q’:
Is the performance value of the loop (Typically >6)*
* For vehicle classification > 12 is appropriate
OPEN CIRCUIT
- This message is displayed if the loop is open circuit
SHORT CIRCUIT
- This message is displayed if the instrument identifies a short circuit
Loops and loop feeder cables are all part of the in-pavement loop circuit and an extension of the vehicle
detector circuitry. A suggested analysis procedure is to commence at the detector and progress
backwards to the actual in-pavement loop in compartmentalized steps. It is important for the ‘Q’
calculation to evaluate the complete in-pavement circuit including the loop PLUS the feeder cable
(refer to notes herein concerning calculation of ‘Q’).
Inductance Schedule – Measurement Tolerance
