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Thread: Using a USM for a speed input

  1. #1

    Default Using a USM for a speed input

    I have not been able to work this out from the documentation supplied, is it possible to use a USM input for a wheel speed sensor to provide an alternative to the GPS based speed input? I will be running my car at a regularity event in August and I expect to be required to disconnect the GPS input to my dash as in car timing is not permitted and removing the GPS is likely to be the only way to convince the organisers that I do not have it available to me.

    Conversely at this event they also have a quite low pit lane speed limit, which is enforced by applying penalty laps to your team for breaking it. Due to the scoring system used at this event a single penalty lap in the day (The event is a 6 hour relay regularity) effectively puts a team out of the running for a good finishing position so I am keen to have an alternative speed input available in case I have to disconnect the GPS using the sensors I already have.

    I have two different hall effect type triggers I can use as wheel speed inputs plus I have a channel I can spare on my USM (It is in use but not logging anything essential so I can re purpose it for speed if this is possible)

    Can ayone advise how to configure a hall switch square wave pulsed input as a wheel speed input on a USM?

  2. #2

    Default Re: Using a USM for a speed input

    I don't see any reason why this wouldn't work. Just be sure to NOT use port #4 on the USM as this input does not have the appropraite input for that type of sensor.

    Below information is directly out of the USM instructions,

    Sensor Cable to USM Terminal Strip

    After connecting the sensor cables to the sensors, we can now terminate the sensor cables at the USM terminal strip.

    Remove the 6 screws from the lid of the USM. Inside Inside are four terminal strips, corresponding to 1-4 on the numbered housing lid and channels 1-4 in the setup software.

    Strip approximately .250” / .635cm of jacket from each sensor wire.

    1. Determine the power requirements of the sensor (5V or 12V)
    2. Insure the strain relief is slid over the sensor cable, then loosen the appropriate screws on each terminal strip
    3. Connect the appropriate sensor wires and tighten each terminal strip wire screw (power, ground, signal etc.)
    4. Install the strain relief cable nut and bushing
    5. Reinstall the housing lid and screws

    Adding USM Sensor Channels to DatalinkII Software

    1. Connect the Racepak serial communication cable between your PC and the data logger
    2. Power up the data logger
    3. Open the DatalinkII software and the Configuration file using the command File->Open Car Configuration from the main menu
    4. Select Edit, then Read Vnet Config located in the main menu selection
    5. When selected a Message Log dialog box will be displayed and the read Configuration process will be started. When completed the following Message Log dialog box will be appear as shown
    6. The message Devices Read Successfully should appear at the bottom of the dialog box indicating the read was successful.
    7. Select OK
    8. Select Save in the DatalinkII Main Menu

    This action will automatically add the four sensors channels from the USM, to the Configuration file, as shown. The AMod Chan numbers correspond with the numbers molded in the USM lid, above each cable input.

    Note that the Read function adds the 1-4 Channel Buttons regardless if any sensors are connected to the USM.

    Programming Individual Sensor Channels

    As indicated on page 6 of this manual, each of the four sensor channels may be programmed for a variety of sensor usage. Following the Read function completed in the above section, Channel Buttons are added to the Configuration file. Each button represents an individual sensor input.

    Access to each sensor channel programming is gained by placing the mouse cursor over the desired Channel Button and right clicking, which opens a Vnet Input Channel as shown.

    While this window appears to contain a large amout of information, there are two areas used for sensor programming.

    A. Vnet ID: This input box assigns the sensor Channel Name and ID used for data transmission. Since we are transmitting all sensor data over the same two wires, it is necessary to assign a unique ID to each sensor. The sensor channel names are grouped according to their type and location on the vehicle.
    B. Sensor: This input box defines the type of sensor, which in turn automatically programs the calibration, graph scaling values and number of digits to display.

    Programming Sensor Channel Name / Vnet ID

    At this time, locate the sensor Channel Button which corresponds with the sensor to be programmed. For the following example, we are going to suppose a 0-150 psi pressure sensor was installed on Channel 1. As an example, we will program this sensor as an Oil Pressure sensor.

    1. Right click over AMod Chan #1. This will open the Vnet Input Channel Parameter window
    2. Using the pull down arrow found in the Vnet ID input box, locate Engine 1, then select Engine 1
    3. This will expand Engine 1 to reveal a large list of engine sensors
    4. Continue to use the pull down arrow to scroll through the list until Oil Pressure X204 is located
    5. Note that Oil Pressure is automatically assigned as Name

    Programming Sensor Type

    The final action is to select the type of sensor. For this demonstration, we are supposing a 0-150 PSI pressure sensor was installed.

    1. Using the pull down arrow found in the Sensor input box, scroll down and locate and select the 0-150PSI Pressure Sensor
    2. Note this action inserts the type of sensor in the Sensor input area and automatically assigns calibration (Raw Data Values A/B) and the graph scaling values (Minimum / Maximum Values) along with value before and after decimal point

    The last action is to update the changes to the data logger by use of the Send button. This button is found in the lower right corner of the Vnet Input Channel Parameters window. Following selection of the Send button and progress window will open. When the send action is complete, as indicated by the Devices Read Successfully, select the OK button.

    Insure power to the data logger is on, before the Send process. If the PC will not communicate with the data logger, turn the data logger power off / on. If a USB to serial adapter is in use, disconnect the adapter from the PC and reconnect.

    RPM Sensor Inputs –Programming Pulse per Revolution

    By default, the calibration values loaded for RPM sensors will be 1 pulse = 1 RPM (Raw Data Value B). To simplify the programming process, the actual number of pulses per revolution can be programmed by the user, utilizing the Channel Options area of the Vnet Input Channel Parameters window. Engine RPM or Hall Effect sensors triggered by a passing ferrous object (bolt head) or magnet may be utilized.

    To program the pulse per revolution of the sensor in use.
    1. Determine the type of sensor (ferrous or magnet triggered) and provide the appropriate trigger target.
    2. Determine the number of trigger targets (pulses) per revolution.
    3. Using the pull down bar in the Channel Options window, move down to the bottom of the input window and select Pulses Per Revolution.
    4. An input window will open up and to the right. Enter the correct number of pulses
    5. Select the Send Configuration button.

    At this point you should have the input showing values that correspond as RPM of the wheel/shaft.

    To convert this to read as MPH, you will have to following the below steps.

    On paper, calculate a factor/number using the rear gear ratio and the tire rollout with the below calculator

    A= rear gear ratio
    Z= Drive tire rollout in inches

    Z / 12 / 5280 / A * 60 = Factor

    4.56 gear with a 102.58 rear tire
    102.58 / 12 /5280 / 4.56 * 60 = .02130 Factor

    In that input settings window (right click on channel tab that you've labeled you MPH channel to enter window),

    1. Select a appropriate V-Net ID (if you haven't done so yet)

    2. Select Hall Effect Sensor RPM Input for Sensor (by default this sensor is set for 1 pulses per revolution, if using more/less magnets, change the pulses per revolution setting in the Channel Options area in the lower left of the window to reflect the correct amount of magnets you are using)

    3. In the Specify Linear Conversion area enter the below numbers

    a. Raw data value A 0 will become 0

    b. Raw data value B 1 will become Factor from above calculation

    c. Minimum result value 0 maximum 200

    4. Send this window to the unit

    5. Program the dash to display this V-Net ID in the area you wish to have it displayed.

    6. Save the config file.

    You should now have speed in MPH, you will lose the Rpm as that signal is now displaying as MPH.

    Attached Files Attached Files

  3. #3

    Default Re: Using a USM for a speed input

    Thanks Eric, I had largely fumbled through that a few days back and arrived at settings for KMH which agrees quite closely with the GPS speed. The wheel speed is a couple of percent higher than the GPS, which is fine as it is for emergency use at my upcoming event if they make me remove the GPS input and for a pi tlane speed display I would rather it read a little high.

    I would have to look over my setting again to see if I arrived at them in the same way as you suggest. From memory I used 4 pulses per revolution (my car has four stud wheels and the sensor is reading the back of the studs) and then calculated the rolling radius of my tyres to determine revolutions per kilometer and then worked it out from there to give a conversion factor.

  4. #4

    Default Re: Using a USM for a speed input

    Can anyone give me the formula so my dash will read kph not mph?

  5. #5

    Default Re: Using a USM for a speed input

    From memory (I have not used the software in a bit) you need to create a metric car config file (I assume you want the GPS speed to read in KMH rather than a USM input as I had) A metric config file will have the GPS speed in KMH.

  6. #6

    Default Re: Using a USM for a speed input

    Hi. No I am wanting a formula to use my USM to display speed in KPH not MPH as above.

  7. #7

    Default Re: Using a USM for a speed input

    I had not looked in here for some time (I sold my dash about a year ago)

    I am having real trouble recalling how I did it. But from memory I worked out how many pulses per kilometer, divided that by 60 (To work out how many pulses per second at 60KMH, which is one KM per minute) and then had to work out a divisor on the number of pulses per second at 60KMH to produce an output of 60 "RPM" I used 60KMH for the conversion as it is easiest to calculate given 1KM per minute so a simple divide by 60 applied to work out pulses per second.

    That "RPM" figure I used on the dash with units in the dash of RPM (To match what the software is calculating) but a KMH tag on the display. It was pretty accurate.

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