Temperature and humidity monitoring and rangefinder principle analysis
Laser rangefinders generally use two ways to measure distance: the pulse method and the phase method. The process of pulse method distance measurement is like this: the laser light emitted by the rangefinder is reflected by the measured object and then received by the rangefinder, which records the round-trip time of the laser light at the same time. Half of the product of the speed of light and the round trip time is the distance between the rangefinder and the object being measured. The accuracy of the pulse method of distance measurement is generally about +/- 1 meter. In addition, the measurement blind spot of this type of rangefinder is generally about 15 meters.
Laser rangefinding is a distance measurement method in the light wave rangefinding, if the light propagates in the air with speed c in A, B two points between the round trip once the time required for t, then A, B two points between the distance D can be expressed as follows.
D=ct/2
In the formula:
D - the distance between the two points A, B at the measurement site; and
c - the speed of light propagating in the atmosphere; and
t - the time required for the light to travel to and from A and B once.
As can be seen from the above formula, to measure A, B distance is actually to measure the light propagation time t. According to the different methods of measuring time, laser rangefinders can usually be divided into two forms of pulse and phase type measurement.
Phase-type laser rangefinder
Phase-type laser rangefinder is a radio frequency, the laser beam amplitude modulation and determination of modulated light to and from the measurement line once the phase delay, and then according to the wavelength of the modulated light, the conversion of the phase delay represented by the distance. That is, the indirect method of determining the time required by the light by round-trip line measurement, as shown in the figure.
Phase-type laser rangefinder is generally used in precision ranging. Because of its high accuracy, generally millimeter scale, in order to effectively reflect the signal, and make the determination of the target is limited to a specific point commensurate with the accuracy of the instrument, for such rangefinders are configured with a reflector known as the cooperative target.
If the angular frequency of the modulated light is ω and the phase delay produced by one round trip over the distance to be measured D is φ, the corresponding time t can be expressed as:
t=φ/ω
Substituting this relationship into (3-6) the distance D can be expressed as
D=1/2 ct=1/2 c-φ/ω=c/(4πf) (Nπ+Δφ)
=c/4f (N+ΔN)=U(N+)
Eq:
φ - the total phase delay produced by the signal traveling to and from the survey line once.
ω - angular frequency of the modulating signal, ω = 2πf.
U - unit length, the value is equal to 1/4 modulation wavelength
N - the number of modulating half-wavelengths contained in the measurement line.
Δφ - the part of the signal traveling to and from the line that produces less than π phase delay at a time.
ΔN - the fractional part of the modulating wave contained in the line that is less than half a wavelength.
ΔN=φ/ω
In the given modulation and standard atmospheric conditions, the frequency c / (4πf) is a constant, at this time the measurement of distance becomes the measurement of the number of half-wavelengths contained in the measurement line and less than half a wavelength of the fractional part of the measurement of the measurement of the N or φ, due to the development of modern precision machining technology and radio phase measurement technology, has enabled the measurement of φ to achieve a very high degree of accuracy.
In order to measure the phase angle φ of less than π, can be measured by different methods, usually applied * more than the delayed phase measurement and digital phase measurement, the current short-range laser rangefinder are used to obtain the φ of the digital phase measurement principle.
From the above mentioned general circumstances phase type laser rangefinder using continuous emission of laser beams with modulation signal, in order to obtain high precision ranging also need to configure the cooperation target, and the current introduction of the handheld laser rangefinder is a pulsed laser rangefinder and a new type of rangefinder, it is not only small, light weight, but also the use of digital phasing pulse spreading subdivision technology, no need to cooperate with the target to achieve millimeter-level accuracy, the measuring range has been More than 100m, and can quickly and accurately display the distance directly. Is a short-range precision precision engineering measurement, housing construction area measurement in the * new length measurement standard apparatus. Now the application of * more than leica company produced DISTO series of handheld laser rangefinders and Touyad Trueyard laser rangefinder telescope.
