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VELOCIMETER (TIME GATE)

The Velocimeter (Time Gate) is a very precise electronic device that calculates the time it takes for an object to pass in front of an infra-red beam a few millimeters before impact. The time in milliseconds and the length of the object are then used to determine the velocity.

The Velocimeter (Time Gate) is a tool that will let you know if your impact reached the desired speed. Without this tool or a simulator it would be impossible for you to know the precise energy level of the machine at the time of impact. It is also used to determine the friction level of the testing machine.

The Velocimeter (Time Gate) is a very precise electronic device that calculates the time it takes for an object to pass in front of an infra-red beam a few millimeters before impact. The time in milliseconds and the length of the object are then used to determine the velocity. Velocity(meter/second) = object(milimeter) / time (miliseconds) The object that cuts the infra-red beam is called the flag. The flag is a small aluminium or steel plate of a prefered thickness of 0.020 to 0.100 inches. The width of the flag that we recommand is 25.4 mm. It is important to verify this value to be sure that your calculation of velocity is accurate.

The Cadex velocimeter (Time Gate) is available in different models. We use only the highest quality circuit boards to reduce wiring, increase presicison and durability. From the circuit board, you have access to choose the normally stat of the output signal. (see figure 2 and 3) The system is calibrated dynamically for a constant reading. No UPS device needed. The system has been designed with a high quality power supply that can take various voltages and even if your electricity input is unstable, the unit will not modify the output reading.

The Time Gate Box is only required for those who do not have a computer. The box receives and displays the information captured by the time gate. Time Gate Box Dimensions Parameter Dimension Unit Height 165 mm. Width 165 mm. Thickness 30 mm. Weight 800 gr. Front and Rear panel material : Aluminium Box Construction : Aluminium Electrical Caracteristics Parameter Min Typ Max Unit Power Consumption - - 6 Watts Operating Voltage Input 6 9 15 Volts A.C. Operating Temperature -10 20 85 Celcius Storage Temperature -30 - 60 Celcius Time Gate Model for Monorail Machine Time Gate Model for Twin Wire Machine Parameter Dimension Unit Height 49 mm. Width 64 mm. Int.Width 38 mm. Length 105 mm. Int Length 47 mm. Parameter Dimension Unit Height 49 mm. Width 127 mm. Int. Width 101 mm. Length 154 mm. Int. Length 99 mm. Other Caracteristics Cable length Custom Distance between transmitter and receiver regular = 40 mm. custom = up to 100 mm. available Construction Aluminium Internal Electrical Caracteristics Parameter Typical values Units Internal Supply Voltage 1-2 see figure beside V.D.C. Normally High Voltage Output 2-3 5 ? 0.2 V.D.C. Normally Low Voltage Output 2-3 0 ? 0.2 V.D.C. Transmitter voltage between A & K (high) 1.3 ? 0.1 V.D.C. Transmitter voltage between A & K (low) 1.3 ? 0.1 V.D.C. Receiver voltage between C & E (high) 4.9 ? 0.1 V.D.C. Receiver voltage between C & E (low) 4.9 ? 0.1 V.D.C. Repeatability 0.005 ms. System precision 0.005 ms. Digit display XX.XX ms. Calibration precision 0.001 ms. 1 The supply voltage must be adjusted to 5.00 Volts or 5.01 Volts D.C. as during the calibration ajustment sequence. 2 Any change to the power supply will modify the calibration of the unit. It should be returned for calibration to manufacturer company Cadex inc. technical support. 3 The voltage of the high and low states is determine by the power supply voltage. This caracteristic is valid for transmitter and receiver voltage. The following picture shows the different states of the output signal from the velocimeter system. Figure 3

	It is important not to touch the optic sensors. The calibration could be upset.

Two output signals can be selected from the back of the Time Gate box: Latched pulse Free pulse

The latched pulse output will send only one pulsation at a time. For example, if during an impact test, the impactor bounces a few times and passes more than once in front of the infra-red beam, you will receive only the first signal. After an impact, the display will lock in place the last result. To unlock the latched output, press the reset button in front of the Time Gate box. The display will show 00.00 ms if the gate is properly connected at the back. If the display does not reset simply check the gate connections and turn the system off and then back on. If everything is OK a green light in front of the box lets you know that you are ready for the next acquisition. The free pulse output will allow you to measure every event in real time acquisition. This output is used for the calibration sequence and in the measurment of the coefficient of restitution. In this case, the display will show the time of the first IR cut even if there is more on the output.

In order to calibrate this system correctly, you must have a propoller with pitch of 18? with very precise dimensions. The power supply DC should be adjusted before calibration to 5.00 ? 0.01 V.D.C. than has a propeller spin between 700 and 900 RPM and no less than 650 RPM.

Time Gate calibration schematic

Figure 6

Now, with a precise scope system or using data acquisition software you will be able to read the output signal to define de T2 value (see figure 7). With the RPM value and using the formula below, you will define the theoritical value for T1 to compare with the T1 real time measurment. Time (in milliseconds)= ((60 minutes / speed (RPM)) / 360?) * 18 degrees (pitch) * 1000

Figure 7

When the calculation is done, you have to use this theoritical value to compare with a real time acquisition of the system and it will show you if the velocimeter is calibrated correctly. If the value variation is more than ? 0.02 ms. you should change the adjustable potentiometer on the internal board until you find the best match. We strongly recommanded that you do not try this calibration by yourself unless you perfectly understand the whole procedure or you have the knowledge/expertise required for these manipulations.

In our line of electronic products, we offer two different model for the velocimeter or time gate system. These two models are made for any impact drop device or for any velocity less than 20 meter/seconds. The first model is the complet unit box with digital display of time in miliseconds and come with the infra-red beam device that could be install on any machine. This product is independant from any other source and have two output possibility (latched and free pulse). ITEM # 5012 The second model is a infra-red beam device assemble with a small electronic circuit board internally. The signal transportation and the powering of the unit is made with a cable of 3.6 meter long with a D-SUB 9 female connector (see pins description below). No display has been made for this model but you need to be connect to a data acquisition system. The power supply is not include in the unit, so you have to use the one of that data acquisition card to have work properly but it will be important to verify the power source because the calibration was done at 5.00 ? 0.01 VDC. If you have anything else, please specify this at the Cadex specialist when order this model. ITEM # 5013

D-SUB 9 female connector

Pin # 1 2 3 4 5 6 7 8 9 Description NC NC NC Led A NC Led K Com Trigger 5 VDC

The model #5012 can't be use with any other connection than is time gate box because the IR don't benefit of a internal circuit board inside the IR device. The model #5013 can't be connect to the time gate box controler. To avoid any problem, we are using different type of connector. For more information about this topic don't hesitate to let us know your question.