The test equipment discussed in this section is limited to that equipment which is most critical in making the measurements discussed in this document. All other test equipment shall be of laboratory instrumentation quality. All test equipment shall be provided with instruction manuals.
The tripod shall provide sturdy support and multi-axis adjustment, including a hinge-like joint that permits the lidar UUT to be tipped 90º to one side.
Two baselines shall be established, probably outdoors, to check the lidar unit’s range feature at zero target speed (see fig. 2). Each baseline shall have at one end a fiduciary mark by which the lidar unit can be positioned, and at the other end a well-anchored flat target perpendicular to the line of sight along the range. The target might be a building wall or a sign on a sturdy post. It will be helpful if the target is retroreflective. The exact target area and the working height of the lidar unit shall be decided and recorded first. Then, the distance shall be surveyed along the line of sight1. One baseline distance shall be in the range of 6 m (20 ft) to 30 m (100 ft). The other baseline shall be at least 90 m (300 ft). (Note: a routine survey may give you horizontal distances only. That information cannot be used directly because the lidar device does not provide any means to measure the angle of elevation. Therefore, the baseline data must be complete enough to determine the heights above or below a horizontal reference plane of the targets and a UUT and allow the line-of-sight distance to be calculated to within 1 cm (0.4 in)).
The long-range target consists of a rectangle of white retro-reflective material, centered on a circular black background, (see fig. 6). The retroreflective material shall be "engineering grade," Type I as specified in ASTM D 4956. The rectangle shall measure 300 mm ± 5 mm horizontally, by 150 mm ±5 mm vertically. The background shall be matte black poster board, 610 mm ±3 mm in diameter. The retroreflective material may be affixed to the background with hook and loop material, (e.g., Velcro 2) or otherwise.
The beamwidth measurement apparatus is an outwardly simple custom-made device that must meet the optical performance required in §5.6. Mechanical details may vary, so long as the optical performance is met.
The environmental chamber or chambers shall produce air temperatures and humidities that meet the requirements of §2.7.1 and §2.7.2 while shielding the UUT from direct heating or cooling air currents. The temperature of the lidar device shall be measured with a thermometer that is separate from the sensor used to control the chamber air temperature and has an uncertainty no greater than ±1 ºC (±2 ºF). Likewise, humidity shall be measured with a hygrometer that is separate from the sensor used to control humidity and has an uncertainty no greater than ±2 %.
The target speed simulator consists of a computer with IEEE-488 and counter-timer cards; a digital delay generator with an IEEE-488 interface-bus option; a receive-send module to trigger the delay generator and generate a return laser flash; IEEE-488 bus, 50 Ω coaxial and miscellaneous cabling; and the software program VS.EXE that was written at NIST.
The simulator must respond to the periodic flashes from the lidar UUT and return laser flashes with properly calculated delays. The simulator must simulate speeds from 0 km/h to 320 km/h (0 mph to 200 mph), approaching and receding. The speed of a simulated approaching vehicle should be treated as positive; the speed of a receding vehicle should be considered negative.
The simulator shall be based on a speed of light in air of 299,705,663 m/s. This value is correct at zero elevation and T = 0 ºC. Changes in temperature and pressure will seldom affect the speed reading by more than one part in 104. The error will be in the motorist's favor for temperatures and elevations higher than the reference conditions
The counter-timer interface card functions primarily to determine the pulse repetition rate of the lidar UUT. It does not resolve the delay times generated by the digital delay generator. The card that has been used has a 5 MHz frequency source and a programmable timing chip with 5 separate 16-bit counters.
The digital delay generator must have the following characteristics:
4.10.1 Bus Reprogrammable - accept reprogramming of the delay time from the digital computer by a means such as the IEEE-488 interface bus.
4.10.2 Reprogramming Speed - accept reprogramming in less than 2.5 ms, so that the computer hardware and software plus the digital delay generator can simulate a moving target at lidar unit’s PRRs up to 390 Hz.
4.10.3 Delay Ranges - generate delays ranging from tbase + 0 μs to at least tbase + 5 μs, where tbase is a fixed delay relative to an external trigger of no more than 100 ns. The delay must be settable with a precision of at least 50 ps, and have an rms jitter of no more than 100 ps.
The pulse generator shall be capable of producing 10 V p-p across a 50 Ω load impedance, with rise and fall times of less than 1 μs and PRRs of 200 pps to
The sawtooth wave generator shall be capable of producing 10 V p-p across a 50 Ω load impedance. It shall also be capable of producing a sawtooth waveform that has a negative-going ramp and a positive-going trailing edge with a rise time of less than 1 μs. It shall be frequency adjustable over a range of 200 Hz to 10 kHz.
Injection of pulse and sawtooth waves into the power line of the UUT requires the circuit of figure 3. In the prototype, the capacitor was 10 μF ±10 %, 200 V dc. The inductor had an iron core; it was in fact the secondary of a filament transformer whose primary circuit was open. The inductor's impedance, given by Z = Vrms/Irms with an applied sine-wave voltage, varied from 45.8 Ω at 200 Hz to 309 Ω at 10 kHz. Its inductance, determined by L = Z/(2πf), varied from 36.4 mH at 200 Hz to 4.9 mH at 10 kHz. The inductor used must have an impedance of at least 40 Ω over this frequency range.
The FM signal generator shall be capable of producing 20 mW output power at frequencies from 30 MHz to 500 MHz and shall have an audio frequency modulation variable from 500 Hz to 5 kHz, a 50 Ω output impedance, a maximum standing-wave ratio of 1.2, and a variable output level. It shall also have a deviation meter or calibrated control for determining the peak frequency deviation with an uncertainty no greater than 10 %.
The AM signal generator shall cover the 25 MHz to 30 MHz frequency range, be capable of producing at least 20 mW output power with 99 % modulation depth over frequencies from 500 Hz to 5 kHz, have a 50 Ω output impedance, and have a maximum standing-wave ratio of 1.2. The generator should include a digital frequency counter having an uncertainty no greater than 1 part in 106 and a monitor or calibrated control for determining the modulation depth with an uncertainty no greater than 10 %. If an integral frequency counter is not provided, a separate frequency counter having the required accuracy shall be provided.
The LISN, constructed as in figure 5, serves to couple the signal from the radio-frequency signal generator into the power line of the UUT, while the UUT is also receiving its power from the dc supply.
The power meter shall have 50 Ω feed-through detectors for measuring both the forward and reflected power over a frequency range of 20 MHz to 500 MHz. It shall have the ability to handle powers up to 50 mW with an uncertainty of no greater than 10 %.
The slide whistle, a wind instrument with a notched hollow tube and a variable displacement, shall be capable of producing audio frequency notes form 500 Hz to 3 kHz.
A digital sampling oscilloscope (DSO) is required for routine setup and adjustment of the simulator (see fig. 1) and for detailed verification that the simulator is working correctly. It shall have an analog bandwidth of at least 500 MHz and a minimum sampling rate of at least 2 gigasamples/sec (2x109). It shall have at least two input channels. Each channel shall have 50 Ω input impedance and an auxiliary high-impedance probe. The DSO shall have automatic measurement capability for such parameters as the interval between pulses, amplitude, and frequency. It shall have Fast Fourier Transform capability. It shall have a repetitive single-shot mode which can trigger on one pulse, store 2000 or more points on two channels, then repeat when a new trigger occurs after 2 ms so that a train of 80 or more two-channel recordings is made. When operating in repetitive single-shot mode, it shall record the time of each trigger; for this purpose, the first trigger may be taken as time = 0.0, or time may be recorded as clock time (year, month, day, hour, minute, second), so long as the trigger times can be retrieved to a precision of 0.1 ms or less.
1 If baselines are set up using electronic surveying equipment, a question may arise concerning the "certification" of the electronic distance-measuring device. There is no centralized program in the United States by which such equipment can be certified. It is a surveyor's responsibility to check his equipment against known monuments or other instruments, and to keep records. There is a national program for the establishment of calibration baselines; their use is optional. Two publications of the National Oceanic and Atmospheric Administration on this topic are: NOAA Technical Memorandum NOS NGS-8. Establishment of Calibration Base Lines by Dracup, Fronczek, Tomlinson, and Spofford, 1994, 17 pp., $1.60; NOAA Technical Memorandum NOS NGS-10. Use of Calibration Base Lines by Fronczek, December 1977, reprinted 1980, 38 pp., $2.80. Other information, including a list of baselines, is on the World Wide WEB at http://www.ngs.noaa.gov/CBLINES/calibration.html. Purchase of the publications can be arranged by email to email@example.com, or by calling 301-713-3242, Monday – Friday, 7:00 am to 4:30 pm eastern time, or by mail to National Geodetic Information Branch, N/CG-17, 1315 East-West Highway, Room 9554, Silver Spring, MD 20910.
2 Certain materials are identified in this paper in order to adequately specify the experimental procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials are necessarily the best available for the purpose.