Method for generating a time delay
In a Time Domain Reflectometry (TDR) measurement system including a measurement probe and an electronics assembly, a method for generating a time delay between transmit and receive pulses for capturing measurements in a given measurement cycle, comprising initiating first relatively slow and second relatively fast time-dependent non-linear ramped waveform functions associated with transmit and receive signals, respectively; and initiated at a time prior to initiation of the first time-dependent non-linear ramped waveform at a second time t 0 ; comparing outputs of the first and second time dependent non-linear ramped waveform functions and activating a receive signal to measure a data point along the waveguide at a third time t 1 when the outputs of the first and second time-dependent non-linear functions are equal; wherein the first and second time-dependent non-linear ramped functions are configured such that their waveform characteristics produces a time delay between time t 0 and time t 1 that is a linear function of time.
1. In a Time Domain Reflectometry (TDR) measurement system including a housing and an elongate measurement probe and an electronics assembly comprising a transmitter for transmitting a signal to the elongate measurement probe and a receiver for receiving at least a return echo from the signal upon encountering a change in impedance to thereby determine a position of a medium in relation to the elongate measurement probe, a method for generating a time delay between transmit and receive pulses for capturing measurements in a given measurement cycle, the method comprising:
said electronics assembly initiating a first time-dependent non-linear ramped waveform function and a second time-dependent non-linear ramped waveform function associated with transmit and receive signals, respectively;
wherein the second time-dependent non-linear ramped waveform function being a relatively slow waveform in relation to the first time-dependent non-linear ramped waveform function, and initiated at a first time prior to initiation of the first time-dependent non-linear ramped waveform at a second time t 0 ;
comparing the output of the first time dependent non-linear ramped waveform function and the second time-dependent non-linear ramped waveform function;
activating a receive signal to measure a data point along the waveguide associated with a localized impedance at a third time t 1 when the outputs of the first and second time-dependent non-linear ramped waveforms are equal;
wherein the first and second time-dependent non-linear ramped functions are configured such that their waveform characteristics produces a time delay between time t 0 and time t 1 that is a linear function of time.
2. The method according to claim 1 , further comprising,
in response to a determination that the outputs of the first and second time-dependent non-linear ramped waveforms are equal, resetting the first time-dependent non-linear function to a known value and repeating the comparison between the first and second time-dependent non-linear waveform functions until the outputs of the first and second time-dependent non-linear ramped waveforms are determined to be equal, wherein, in response thereto, actuating a receive signal to measure another data point along the waveguide associated with a localized impedance; and repeating said steps to thereby generate a series of time delays.
3. The method according to claim 2 , further comprising generating a series of linearly increasing time delays by linearly increasing the time between the said reset of one of the time-dependent non-linear waveform functions.
4. The method according to claim 2 , wherein the second time-dependent non-linear ramp waveform function is reset at the end of a measurement cycle, and the wherein generation of a series of time delays is repeated.
5. The method according to claim 4 , wherein a profile of an echo signal is developed and used to determine the position of the medium by the elongate measurement probe.
6. The method according to claim 1 , wherein the first and second time-dependent non-linear ramped waveform functions are exponential functions.
7. The method according to claim 6 , wherein the second time-dependent non-linear ramped waveform function is given as
V
-
1
=
V
cc
×
(
1
-
e
-
t
t
s
)
wherein:
V 1 is a charging voltage across a capacitor of said electronics assembly;
Vcc is the supply voltage,
t is the elapsed time since application of the supply voltage, and
ts is the RC time constant of the RC charging circuit; and
wherein the first time-dependent non-linear ramped waveform function is given as
V
2
=
V
cc
×
(
1
-
e
-
t
-
t
0
t
f
)
wherein:
V 2 is the charging voltage across said capacitor,
Vcc is the supply voltage,
t is the elapsed time since application of the supply voltage,
t 0 is the time at which the transmit signal is generated,
and t f is the RC time constant of the RC charging circuit.
8. The method according to claim 1 , wherein the first time-dependent non-linear ramped waveform function is configured as a 40 Hz square wave signal; and
wherein said second time-dependent non-linear ramped waveform function is configured as a 4 MHz square wave signal.