9
LTM-1000 Main Circuit Board Layout
These drawings provide a functional block representation of the in-pavement loop tester. The device
has a single 9 Volt battery source. The power management circuitry converts the 9volts to 12volts and
5 volts. The 5VDC source is utilized by the microcontroller and logic circuitry. The 12VDC source is
utilized by the loop drive and sense circuitry. An LCD display provides status and measurement data
to the user and functions are selected via touch pad circuitry mounted on the front of the device.
This circuitry, which is driven by the microcontroller excites the in-pavement loop to operate at its
‘tuned’ or resonant frequency. This excitation is a function of the loops resistance, inductance,
capacitance, susceptance and other minor electrical characteristics. The microcontroller searches for
resonance and then computes the related values of resistance, inductance and ‘Q’ within the resonance
equation.
The tester has a high voltage generation circuit which produces 500Vs for approximately 1 second in
order to verify that the insulation integrity (resistance) is greater than 100meg ohms to earth.
The tester incorporates a tuned input circuit connected via a coil located within the external probe.
This enables the operator to search for an electromagnetic field with a frequency within a typical loop
frequency range of 40-140Khz.
Microcontroller
|
LCD DISPLAY
MODULE
|
Touch PAD input
Loop Resonator Circuit
This circuit energises the loop
to its resonant frequency –
enabling measurement of
inductance, resistance, tuned
frequency and ‘Q’
Loop Locator Circuit
This circuit detects and
responds to electromagnetic
energy frequency in the range
of 40Khz to 140Khz (typical
loop resonant excitation
frequency)
Insulation Integrity
High Voltage Generation
Circuit
500V For approx. 1 second
Resistance > 100Megohm
9VDC Battery
12VDC & 5VDC
‘switch on/off’
