Within the data acquisition System, there are two distinct types of tests:
- Dynamic tests
- Special tests
The dynamic test refers to the systematic measures taken with the instrumentation while the vehicle is in motion. When carrying out this kind of tests, the sensors being measured have to be previously defined, up to a number of 240 per test. Besides, a results file (ASCII) is created to include all the variables required for the analysis of curves, such as pavement temperature, environmental temperature, number of cycles, transverse position, vehicle speed, date and time. Dynamic tests are activated automatically.
They can be activated by means of three different events, which are selected when the test is being scheduled. These three events are the following:
- Number of cycles. The test begins when the vehicles cover a predetermined number of cycles.
- Time. The date and time of the beginning of the measurement are indicated.
- Temperature. It begins when the pavement temperature (defined by the user) reaches a certain value.
The presence of staff at the facility is not required for this kind of tests, which are performed 24/7. When the event that triggers a test takes place, the Control Computer instructs the PLC Master to position the vehicles on the conditions required for the test (speed and transverse position).
Once the vehicles are placed in the right position for the scheduled test, the Control Computer sends a set of low level commands to each MGCplus connected to the Ethernet network. These commands transfer .MPR files with the recording parameters to the device and activate them to be prepared for the acquisition process.
There is one optical sensor connected to each MGCplus to use for triggering the measurement. When the vehicle selected pass by the optical sensor which activates the beginning of the data collection, and is stopped after a period of time, defined in the recording file. Figure 9.
When the vehicles complete one cycle from the beginning of the data collection, the Control Computer connects to the MGCplus devices to transfer the data collection file that has been created from the DAQ to the Control Computer and convert it into ASCII format by means of the Catman control ActiveX.
All of that has been programmed inside a Visual Basic script which also realizes a signal processing to change time to distance, cut and resample in order to store the number of samples that are interesting for analysis.
After that the Control Computer has to put all the data together in the results file (ASCII), the data from the PLC System regarding the vehicles (speed, transverse position) and the data from the data acquisition System regarding the sensor measurement process.
Once every piece of data is stored, the test finishes and the PLC System in charge of the steering of the vehicles regains control. This test can be scheduled cyclically depending on the number of cycles, after a determined period of time or when the desired temperature values occur.
The special test refers to other kind of measures that would be carried out with the instrumentation without using the whole Control System, directly with the MGCplus devices.
We would like to highlight the following three types of tests as special tests:
- Temperature traces. There are two Siemens ET 200 as part of the PLC System in which have been connected the analog outputs of the MGCplus to have a continuous pavement and environmental temperature registered. These are used to analyze not only the instrumentation but also the damages of the pavement.
- Manual Start. These tests can be performed not only with vehicles in motion but also with vehicles stopped. They begin when a trigger is sent. This kind of test is used to study in detail some specific variables when the vehicle is passing by and, unlike the dynamic tests; they are made with a sample frequency up to 3000 samples per second. This test is also used to measure the response of one or various sensors to equipment other than the test vehicles, e.g. FWD devices.
- Start by optical sensor. It has the same features as the Manual Start test, but, in this case, the measurement is triggered by one of the optical sensors on the test track.