With the lidar unit in hand, the test engineer shall review the instructions and the markings on the controls to verify that the controls operate as explained in the manual and consistently with their markings. The simulator or normal traffic may be used for input data. It is permitted for controls to have secondary functions beyond those marked; in these cases, there is a particular obligation for the manual to be written in plain English and to describe the use of the controls accurately.
While it is impossible for this test to be exhaustive, the test engineer shall look for:
No misleading wording is permitted on the control panel and display, or in the manual. If an undocumented mode does turn up, such as an engineering test mode for instance, the resulting display shall be clearly different from the display in normal speed-measurement mode.
This test applies only to the accuracy of measurements of the distance to stationary targets. Target ranging shall be checked on the two measured baselines. The reference plane on the lidar unit is the front surface (the surface with the lenses) unless the manufacturer has clearly defined a different reference (see fig. 2). Set the lidar unit at the predetermined height (§4.3) and aim it at the correct target area. If the surveyed distance is not an integer number of meters or feet, corresponding to the system of units of the lidar device, make an auxiliary mark a fraction of a meter (or foot) forward of the fiduciary mark so that the range becomes an integer number of units. Repeatedly record the target range or error indication until five range measurements are recorded. All five readings must be correct to a tolerance of ±0.3 m (±1 ft). Perform this test and calculate the arithmetic mean of the readings for each of the pre-surveyed baselines.
Elevate the long-range target (see fig. 6) so that its center, as seen from the lidar UUT, is at least 2 m above the ground or other obstacle. The background should be sky. Determine the greatest range at which the lidar unit can measure the distance to the target. Pay attention to the beamwidth of the UUT and the target's clearance from the ground; be sure that the UUT is ranging to the target and not something else. If a range exceeding 300 m (1000 ft) has been measured and conditions do not permit the UUT to be backed farther away, the test may be stopped. Record detailed observations as the lidar operator moves back from the target, including all distances at which the UUT obtained range measurements and the reason for stopping the test.
Set up the apparatus as illustrated in Figure 7. Note that this figure is not drawn to scale but is dimensioned to verify beam alignment, range accuracy, and beamwidth. Mount the lidar unit under test (UUT) upright on a tripod with the laser beam parallel to the ground (floor) and at the same elevation as the center points of the targets. The tripod mount shall permit the UUT to be rotated so the centerline of the laser beam can be aimed at the center point of each target. To facilitate aligning the laser beam with the target, a small flashlight may be held just above the target. The flashlight must be removed before the test readings are taken. A 60-inch carpenter’s level may be used to help align the front of the UUT with the reference mark.
5.6.1 Beam Alignment.
5.6.2 Range. Aim and record the distances to each of the three targets: TL, TC and TR. Repeat until ten range measurements have been recorded for each target. Verify that the UUT is capable of measuring and displaying the correct range to each target.
5.6.3 Target Discrimination.
5.7.1 Operational Temperature Test. Choose three speeds within the capability of the UUT and store them in a file for use by the simulator software as a "Standard Speed Series." (The speeds should be integer values in the UUT native system of units.) Place the UUT, with the power off, in the environmental chamber and adjust the chamber to the required low temperature, TdLow ±2 ºC (±3.6 ºF). Allow the UUT to reach thermal equilibrium and maintain it at this temperature for 30 min. Prepare the simulator hardware and software so it is ready to run a test. Use protective gloves and remove the UUT from the environmental chamber. Connect the UUT to the standard supply voltage, turn it on, and optically couple it to the simulator. Measure the PRR and then test the UUT at the three simulated speeds. Work quickly, as frost may be forming on the external lens surface. Perform the high temperature test during the same day to dry out the unit.
A simulator test should remain valid despite a thin layer of frost. If the UUT fails to read the simulated speed accurately, repeat the test. The UUT shall meet the requirements of §2.7 within 15 min of operation. Any external frost in itself is not an intended feature of this test, and if it is possible to reduce ambient humidity, this may be done.
Repeat the test just described at the required high temperature, TdHigh ±2 ºC (±3.6 ºF). In the high-temperature case, energize the UUT when it is removed from the chamber, but wait 2 min before performing any measurements, including the test of PRR.
If the UUT is a lidar system, then repeat the test just described at the required low temperature, TsLow±2 ºC (±3.6 ºF).
If the UUT is a lidar system then repeat the test just described at the required high temperature, TsHigh±2 ºC (±3.6 ºF).
5.7.2 Operational Humidity Test. Place the UUT, with the power off, in a humidity chamber. Adjust the relative humidity to a minimum of 90 % at 37 ºC (99 ºF) and maintain the UUT at these conditions for at least 8 h. Remove the UUT from the chamber and bring it quickly to the simulator. If the UUT is a lidar system, wait for the UUT to cool to TsHigh. Connect the UUT to the standard supply voltage, then wait 2 min before performing any measurements. The UUT shall meet the requirements of §2.7 within 15 min of operation.
A simple connection box, as shown in figure 8, will permit meters to be connected for measurement of voltage and current. Comparison with figure 3 will show that this can be the same box used to inject the pulse and sawtooth signals.
Connect the lidar UUT to the adjustable supply voltage and properly couple its optics to the target speed simulator. Switch the UUT on and let it warm up for 2 min at its standard supply voltage. Set the system to consume maximum power. Set the target speed simulator to simulate a vehicle moving at 110 km/h (70.0 mph). Measure the simulated speed with the lidar unit. Decrease the lidar unit’s supply voltage by 0.2 V and again measure the simulated speed. Continue to decrease the supply voltage and measure simulated speed until the low voltage alert is activated. Record the supply voltage level. Send each reading to the computer file, annotated by the voltage at which it occurs. No erroneous speed reading should occur. Increase the supply voltage until the low voltage indicator is deactivated, and again measure the simulated speed to verify that the UUT reads 110 km/h (70.0 mph).
Also, for a battery powered lidar device designed to accept a 12 V automotive adapter, verify that when using this adapter the device works properly down to its low voltage alert level. The lowvoltage alert levels are specified in §2.8.
Use the setup as in the previous section with a meter to monitor the supply voltage to the lidar UUT. Determine the working voltage range according to §2.9.
5.9.1 Pulse Repetition Rate. For units capable of a fixed PRR, set the simulator to measure PRR. Step through voltages as in §5.8, reaching the high and low limits according to §2.9 while noting the voltage and PRR. Be sure to record all digits of the PRR. The PRR shall not vary by more than 0.1 % from its value at standard supply voltage.
5.9.2 Range and Speed. In this part, the simulator software can be used to record the data. Prepare a table of distance-speed combinations according to the approach in §5.11. Set the simulator for normal speed simulation, including the description of the UUT. Next step through the voltage range as in §5.9.1, setting a different distance and speed at each voltage step. The UUT shall not display any erroneous speed readings. A blank display is not considered an erroneous reading. If a blank occurs, the test must be repeated, and an accurate non-blank speed must be obtained at each step.
5.10.1 Display Readability. Establish a simulated target speed and verify that the display is clearly readable when used as intended by the manufacturer.
5.10.2 Speed-Display Lock. For convenience, these tests may be performed in conjunction with the display clear test of §5.10.3. The lidar device must have one condition under which the display is intended to lock; such as "as soon as a valid target is acquired after the press of the trigger" or "when the trigger is released." Verify that the display locks under the specified condition and not under other circumstances.
5.10.3 Display-Clear Function. Connect the lidar unit to the target simulator, energize it, and establish a simulated target. Press and release the trigger, locking in a speed reading. Turn off the simulated echo. Press and release the trigger a second time. The display should clear. Now operate one of the control switches (speed, range, display intensity, timing mode, etc.) and verify that the display remains clear. Start over by reading the nonzero speed of a simulated target and then repeat these steps for each control switch on the UUT. In the absence of a (simulated) target, no sequence of switch operations shall cause a nonzero speed to be displayed after the display has been cleared.
5.10.4 Internal-Circuit-Test Function. Perform the internal circuit test according to the manufacturer's instructions. This may simply require the lidar unit to be switched off and on. Verify that only the correct readings are displayed, and that all readings are cleared automatically when the test is completed. Repeat the internal circuit test and attempt to actuate the speed lock while the readings are displayed. Verify that no nonzero reading is retained by the display.
5.10.5 Low-speed and High-speed Display Limits. Let "slow limit" be 16 km/h (10 mph) or the lowest speed at which the manufacturer states that his device will operate, whichever is lower. Let "fast limit" be 320 km/h (200 mph) or the highest speed at which the manufacturer states that the device will operate properly, whichever is higher. By definition, these limits are positive or zero. Set the simulator to each of the following conditions and record data. An accurate non-blank reading should be obtained in each case.
5.10.6 Audio Tones and Error Messages. It is not required for the lidar device to emit audio signals. If it does make sounds, test it on the simulator or simply beside a road, and generate a mixture of valid readings and error indications. If necessary, turn on the audio signal. Make written notes of the relationship between the display and the sounds generated. Then continue to generate valid and invalid readings and verify that the relationship is consistent.
5.10.7 Speed Monitor Alert. Verify that the lidar device does not have a speed monitor alert.
5.11.1 Smoothly Moving Target. Begin by noting the stated limitations of the simulator and the UUT. Determine the range of speeds and distances that are available both to the simulator and to the UUT and, thus, can be used for testing.
Record range and speed from the display of the UUT. The simulator software will automatically record the simulated range and speed. No erroneous speed readings shall occur. A blank display or an error message is not an erroneous reading; if the UUT gives a blank display or an error message, repeat the test and adjust the simulator if necessary. It is required for the UUT to give a reading at all settings tested within the working range.
5.11.2 Smoothly Moving Target with Sawtooth Perturbation. A lidar unit can potentially read an erroneous speed if successive laser pulses are not all reflected from the same part of the same target vehicle. It is the user's job to hold the laser device steady, but there is also a need for the instrument to reject bad data based on clues contained in the data set. That is, raw data of range versus time should ideally plot as a straight line; when the raw data deviate from straightness, the speed derived from the data is suspect, and it should not be displayed. The exact criteria for rejecting suspicious data have been a matter of engineering development and are proprietary to the lidar manufacturers. This section will verify that the UUT has some ability to reject suspicious data.
The simulator software has a perturbation feature that permits a periodic disturbance to be added to the normal simulation of a target moving at constant speed. The user must describe the perturbation in an ASCII file, rather than interactively. The file specifies the distance as a function of time by an ordered list of pairs beginning at time 0.0 s. The unit of distance may be chosen as feet or meters. The program interpolates the function linearly between the given points and then applies the appropriate perturbation to the delay of the return laser pulse. The perturbation has a period equal to the interval of the given function. The standard perturbation is defined by the four points listed below. This perturbation is based on a realistic view of what bad data may look like, but it is by no means a basis for writing an error-trapping algorithm.
If entered in just this form, the perturbation is null for 10 ms after the first pulse of the UUT. It then jumps to about 5 ft in 2 ms and ramps back down to zero by the end of the total time interval of 200 ms. It immediately repeats. The test laboratory may optionally shift the perturbation cycle in time. If the perturbation is shifted in time, the total time interval still must be less than the period between laser pulses from the UUT. In general, it might take five points to redefine the function in time-shifted form, and a small change in the function may result because of the way the software splices the end of one cycle onto the beginning of the next. In any event, the software allows the operator to review the net perturbation exactly as it will be applied, pulse by pulse.
In testing with perturbed data, the expected result is "no reading," or perhaps an error message. The procedure that follows includes frequent control experiments to verify that all the wires, switches, and optical alignment are correct, and that an occurrence of "no reading" is indeed a valid rejection of invalid data.
Prepare a list of at least 12 different distance-speed simulator settings similar to that in §5.11.1. Start the simulator and follow its top-level menu to write the PRR, time, and a description of the experiment into a header for a results file. Test the UUT at the first setting, with the perturbation OFF. Record the reading. If no reading is obtained, adjust the setup until reliable readings are obtained; then record one reading. At the same distance-speed setting, and at three other settings, record data with the perturbation ON. Although the simulator software will automatically note that the perturbation is on, the detailed perturbation file(s) shall be kept with the data and printed out for complete documentation. Using the next distance-speed setting, record another reading with the perturbation OFF. Again verify that the simulator and UUT are working. Then, with the perturbation ON, record data at that setting and the next three. Repeat this process until the list of settings is used up. It may be convenient to select a different perturbation file after each grouping of five measurements. (See the previous discussion about shifting the time origin.)
No erroneous readings are permitted. A blank display or an error message is not an erroneous reading.
5.12.1 I/O Port. If the UUT has a computer I/O port, such as RS-232, use the information, software, and cabling supplied by the manufacturer to verify that the port is operational. That is, the lidar unit's I/O port should send data in the manner specified and in the sequence claimed. Exhaustively detailed testing is not required.
5.12.2 Switching Output. If the UUT has a switching output, use the information and indicator box supplied by the manufacturer to verify that the switching output functions as claimed. In a typical instance, the indicator LED shall go off and on in the expected way, and further checking of the circuit and the terminal voltage shall show that the output is sourcing or sinking a current at the times claimed.
5.12.3 Remote Control. If the UUT has a connector for remote control that is claimed to be a computer port of a standard type, use the information, simple software, and cabling supplied by the manufacturer to verify that the remote control function is operational. That is, the lidar unit's I/O port should receive data in the manner specified, and act on the commands issued. If more elaborate proprietary remote control software is sold for use with the UUT, test the functionality of that software with the unit. All functions tested should work as claimed, but testing need not be exhaustive.
5.12.4 Remote Trigger. If the UUT has a remote trigger function, test it with the information and switch box supplied by the manufacturer. Verify that the switch box triggers a measurement in the manner claimed, and that the circuitry of the switch box is consistent with the description in the owner’s manual.
If the unit under test is intended to be connected to an external source of power, then connect the lidar unit to the simulator and to the other test equipment as shown in figures 1 and 3. Activate the UUT and verify that it is interacting with the simulator and correctly measuring the simulated speed.
In §5.13.1 and §5.13.2, the amplitude of the pulse or sawtooth wave must be set with a dummy load in place of the UUT. The dummy load is a 10 Ω resistor with a power rating of at least 20 W. [V2/R = (13.6 V)2/10 Ω = 18.5 W.] The dummy load may be removable, as indicated, or the output may be switchable between the dummy load and the UUT. In the prototype, the dummy load was made from a 10 Ω nominal resistor, with an adjustable tap; since the end-to-end resistance exceeded 10 Ω, the slider was set to give a resistance within 1 % of nominal. A high-impedance oscilloscope probe must be attached across the dummy load. With the dummy load in place, it will show somewhat distorted pulse and sawtooth waveforms. At the fast edges of the distorted waveforms, narrow transient spikes may appear. Although these transients may be an important potential source of interference, they are to be ignored in setting the peak to peak amplitude of the waveforms. Figure 4 shows an oscilloscope display of a distorted pulse. ”Markers“ have been set on the oscilloscope to show the approximate baseline and top line of the waveform.
5.13.1 Simulated Vehicle Alternator Interference.
5.13.2 Simulated Vehicle Ignition, Air Conditioner/Heater Motor, and Windshield Wiper Motor Interference. Connect the sawtooth wave generator and dummy load in place of the pulse generator and lidar UUT. Set the generator’s output frequency to 200 Hz and the waveform amplitude to 1 V p-p or 7.5 % of the standard supply voltage in use (whichever is lower) as measured by the oscilloscope across the dummy load. Remove the dummy load from the coupling circuit and replace it with the lidar UUT. Establish a simulated target of 64 km/h (40 mph) and slowly vary the generator frequency from 200 Hz to 10 kHz and back to 200 Hz. Operate the lidar UUT at 12 or more values of the sawtooth frequency, including 200 Hz and 10 kHz, recording data with simulator software. Verify that no erroneous readings appear.
5.13.3 Simulated Police FM Transceiver Interference.
5.13.4 Simulated Citizens Band (CB) AM Transceiver Interference.
In this test, the lidar device will be tested for potential interference from two types of vehicle- mounted transceivers, and from a hand held transceiver. The lidar shall be operated by a person either seated in either front seat of a patrol vehicle of the type normally used for law enforcement or standing close by that vehicle. This patrol vehicle shall be the same one containing the rf transceiver. In addition to the person operating the transceiver and slide whistle and the person aiming the UUT, it may be helpful to have an additional person to write down readings from the UUT as they show up in the display. It may also be possible to record the readings via a serial link to a computer; in this case, the software must be arranged so that the relevant data for each test are clearly labeled. It may be helpful to steady the lidar with a tripod or other support.
The patrol vehicle shall be located along side a straight road or test track and the UUT shall be used to measure the speed of a target vehicle that is at least 120 m (400 ft) away and traveling at a speed of approximately 80 km/h (50 mph).
When the slide whistle is used, it shall be blown very hard in order to generate strong overtones that modulate the rf carrier at audio frequencies higher than those of the fundamental notes.
5.14.1 Police FM Transceiver Interference Test.
5.14.2 Citizens Band (CB) AM Transceiver Interference. Mount a 4 W minimum output CB transceiver in a typical front seat location and install its antenna as recommended by the manufacturer; or use any vehicle which has a CB installed. Run the vehicle engine at idle. Switch on the CB transceiver, set it to channel 20, activate the push-to-talk switch, and use the slide whistle to generate audio that is coupled into the transceiver via the microphone. Blow the whistle hard and vary the slide position over the entire range while measuring the speed of the distant target vehicle with the UUT. Observe or record the readings from the UUT, looking for erroneous readings. Repeat for channels 1 and 40.
5.15.1 Speedometer-Correction Factor. Establish a measured distance of at least 402 m (1320 feet) on an open, level location away from other moving targets. Drive the target vehicle over the measured distance at a constant speed, preferably using the vehicle’s cruise control, and measure the elapsed time with a stopwatch while recording the speedometer readings. Repeat the procedure twice in each direction, maintaining the same speed for all four runs. Use the stopwatch to determine the target vehicle’s average speed and use this speed to calculate the target vehicle’s speedometer correction factor. The corrected speedometer reading shall be compared with the speed reading provided by the certified radar unit and that of the lidar UUT to determine the accuracy of the UUT.
5.15.2 Speed Test
If requested by the lidar system manufacturer, test the unit for both attended and/or unattended operation.
5.16.1 Attended Operation.
5.16.2 Unattended Operation. Repeat the tests of §5.16.1 supplemented by the manufacturer’s secondary method for verifying that the evidential image correctly identifies the target vehicle and its speed.