Electronic Distance Meters inside - Physikalisch ... · Electronic Distance Meters inside...
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Electronic Distance Meters inside
Trimble’s Geospatial Instruments
Christian Graesser, Martin Koehler, Danderyd, Sweden
1st Workshop – Metrology for Long Distance Surveying @IPQ Portugal – 11 /2014
Overview
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Three different distance meter technologies
developed and produced at Trimble
Calibration traceability
TOF Pulse accumulation digitizer (Trimble Danderyd, Sweden)
Long Range DR, fast
High accuracy
Synchronous
Laser class 1
Technology 1
S6
DR-plus S8 VX
DR-plus
RTS Construction SPS Machine control
Phase Shift (Trimble Jena, Germany)
Medium range DR
Visible laser
Highest accuracy
Technology 2
S8 HP S3
Focus30/35 Focus8 Christian Graesser Metrology for Long Distance Surveying @IPQ Portugal – 11 /2014 5
TOF Single pulse digitizer (Trimble Paris, France)
Medium Range
Super fast
High Accuracy
Clean data
No Post processing
Technology 3
Scanner TX8
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Technology 1
TOF Pulse accumulation digitizer
The “Time of Flight” principle
Pulsed laser versus ambient light
Accumulation of signal
Digitization of the signal
S6
DR-plus
S8 VX
DR-plus Christian Graesser Metrology for Long Distance Surveying @IPQ Portugal – 11 /2014 7
Technology 1
TOF Pulse accumulation digitizer
The „Time of Flight“ Principle
Time difference between transmitting and receiving the pulse
Distance proportional to the “travel”- time t of the laser light
ct
D 2
Transmitter
Receiver
Difficult to see red laser pointer dot under sun light
(1mW)
Our pulsed laser is in the peak
10000x stronger than a red laser
pointer => better visible for the
receiver electronics
Laser still class 1 because in average
the laser power is small.
(only 4 ns on and 40000 ns off)
Pulsed laser
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Setup
IR pulsed laser transmitter
905 nm
Laser class 1
25KHz
pulse rate
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Laser
Transmitter
Receiver
APD
t
Fiber Optics Target
Mirror
Setup
Reference Pulse Measure Pulse
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Length of a Pulse
1.2 m at FWHM
Pulse length: 1.2 m = 4 ns
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Determining a Laser Pulse
Trigger
SHI SHI SHI SHI
SHI = Sample & Hold Integrate
Analogue signal accumulation
To ADC
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Double Sample & Hold
Channel
Processor
Trig Channel A
Trig Channel B
SH1 SH2 SH3
SH1 SH2 SH3 SH4
SH4
APD APD 25 KHz 1 KHz
8 channel
A/D-
converter
1 KHz
20 Hz
Distance Christian Graesser Metrology for Long Distance Surveying @IPQ Portugal – 11 /2014 14
The Sample & Hold Circuit
Reference pulse is measured permanently
alternating with channel A and B
Measure pulse with the circuit of last reference
pulse measurement
Reference pulse
Measure pulse
A B A B A B A B
t A B
Advantages
Better accuracy
Laser has no warming up time
No break by internal reference measurement
Continuous measurement possible Christian Graesser Metrology for Long Distance Surveying @IPQ Portugal – 11 /2014 15
Digitizing
T = 200 ps
Polynomial
f=f(t)
psnTn 200
Reference pulse
Measure pulse
Reference
Polynomial
f = f(t) dt2
mdtTnc
D 2
dt1
dt3
dt4
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Key Performance
Range Prism 5300 m
Range Grey Card 1000 m
ISO 17123-4 1mm 2 ppm
Synch 20 Hz
Pulse accumulation digitizer
Technology 2
Phase Shift Distance Meter
Setup
The Trimble concept of phase shift EDM
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Transmitter
Visible red laser
coaxial
Receiver
coaxial
Phase Shift Distance Meter
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Phase Shift Technology
Red semiconductor laser with 660 nm
7 modulation frequencies around 400 MHz
They contribute all to the fine measurement
All derived from one TCXO (15 MHz)
400 MHz corresponds to fine scale of 0.375 m
Ambiguity solved with difference frequencies of
fine scales
Unambiguity range: 7.3 km
According to ISO 17123-4 0.8mm + 1ppm
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Technology 3
TOF
Single pulse
digitizer
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Trimble TX8
Key Specs Value
Technology Time-of-flight, waveform digitization
Laser wavelength 1550nm
Laser class Class I
Accuracy < 2mm
Precision (1σ) < 2mm for [18%,90%] reflectivity up
to100m
Range Standard: [0.6m, 120m]
Extended: up to 340m
Pulse rate 1MHz, 3 minutes 138 Mpoints
Scanning speed 1M pts/s for standard range
0.4M pts/s for extended range
Scan grid width 0.37 mrad = 18 mm/50 m
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Challenges
Scanning at 1M pts/s with time-of-flight technology
requires to measure distances with single shot
– on a broad variety of materials: from dark coal to shiny pipe
– with different incidence angles
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Compensated distance calculation at 1 MHz –
No postprocessing!
1. Search the pulse
2. Calculate distance
3. Apply calibration
=> Distance
=> Luminance
Distance calculation
Uncompromised performance: TX8 can acquire over 80% of
points on surfaces of 18% to 90% reflectivity to within 2mm of accuracy
up to 100m with 1M pts/s speed
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Example – Rodin Museum in Paris
• Historical building
• Purpose of scanning: renovation preparation
• 230 stations in total: exterior + interior
• 1 day with 2 operators / scanners
• Data processing and registration during field operation
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Example – Rodin Museum in Paris
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Example – Rodin Museum in Paris
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Example – Rodin Museum in Paris
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Overview
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Three different distance meter technologies
developed and produced at Trimble
Calibration traceability
Calibration Traceability Trace-back process
Zero constant Measurements at PTB Braunschweig
Scale factor Calibrated frequency counters
Accuracy of measuring tools in production
Corrections Tools Accuracy
Scale factor Frequency counter ≤ 0.01 ppm
Cyclic error Calibration bar ≤ 0.05 mm
Zero constant Nominal distances
and
Interferometer
2 σ = 0.30 mm
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Trimble Danderyd Interferometer
31
Instrument on the
Interferometer Stand
Laser interferometer Track
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Measurements at the PTB Braunschweig
Interference comparator: 50 m (nominal distances 2σ = 0.1 mm)
Mechanical adaption: calibrated (2σ = 0.1 mm)
Measurement at required sampling points
Forward backwards
each: 5 shots (2σ = 0.1 mm)
Several reference instruments
Trace-Back Procedure
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Scale Correction
Calibration of frequency counters
Accredited calibration laboratory
or GPS-time standard
accuracy 1x10-8 (0,01ppm/year)
monitoring frequency counters by DCF77 time
signal, GPS- or Rubidium time standards
Frequency correction in production
TCXO frequency: 2 Hz of 15 MHz ≈ 0,13ppm
Tra
ce
-back p
rocess
C
alib
rati
on
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Phase Shift Time of Flight
Frequency continuously f0 = 400 MHz Pulse frequency fP = 25,3 kHz
Photo detector fG ~ 500 MHz fG ~50 kHz
Fixed division ratio f0 / fTCXO = 26,7 fP / fTCXO = 0,0013
Input sensitivity 25 mV 20 mV
Continuous zero crossing measurements
External Scale Calibration
60 10
f
ffppm
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1. Measuring reference baselines (PTB) with
reference instruments at predefined sampling points
Forward-backwards, 5-times, final result 2 = 0,2 mm
2. Transfer via reference instrument onto baselines in
production
(Range 2,5 – 50m; accuracy 2 = 0,3mm)
3. Measuring zero constant for each instument
4-6 prism distances, 5-times
4. Verification
Several prism distances, several DR distances
Zero Constant
Tra
ce
-back p
roced
ure
C
alib
rati
on
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