Simcenter Testing Solutions No more tach! Use OBDII to get Engine and Vehicle Speed...

2019-08-29T16:35:31.000-0400

Simcenter SCADAS Simcenter Testlab

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Who wants to spend time setting up a tachometer? You have to mount it on a greasy engine, run cables, etc.

Instead of doing all that, just measure engine rpm or vehicle speed directly thru the OBDII connector of the vehicle! One single connection to the underdash OBD2 connector is all it takes!

It can even be done without a vehicle specific CAN bus DBC file. Due to emissions regulations, certain signals like engine and vehicle speed are legislated to be present on all newer vehicles, and can be read over the vehicle bus directly.

It is easy with Simcenter Testlab Signature 15A and higher, and a Simcenter SCADAS with CAN Bus interface. Note that Simcenter Testlab was formerly called LMS Test.Lab.

Here are the steps:

1. Connect to the SCADAS (9 pin) to the OBDII connection on your car, usually located under the dash:

OBDII port is located under dash

A 9-pin to OBDII cable connects Scadas to vehicle

2. In Simcenter Testlab Signature, make sure "Vehicle Bus" add-in is ON under "Tools -> Add-ins".

Turn on "Vehicle Bus" under Add-ins menu of Testlab

The add-in requires 22 tokens.

3. In "Channel Setup" worksheet, select "CAN Settings" from the pulldown menu in the upper right.

Can Settings.png

Choose "CAN Settings" from the pulldown menu in the upper right of the LMS Test.Lab Signature Channel Setup menu.

4. Set Baud Rate to 500000, select the "Can Device" for the SCADAS frontend, set "Can ACK" to "Active".

Set Baudrate to 500,000, select the CAN card of the frontend, and CAN Acknowledge to Active.

Because the legislated OBDII PID signals are not broadcast by default, it is necessary to request them. This is why CAN Acknowledge is set to "Active".

5. In "DB Path", select the generic OBDII files provided from the directory: C:\Program Files (x86)\LMS Test.Lab {rev}\central\Application Resources\CAN or C:\Program Files (x86)\Simcenter\Testlab {rev}\central\Application Resources\CAN. There are two different files - one with longer descriptive names, one with very short names. Both files contain the same signals, which include Engine and Vehicle speed.

Select the generic OBDII file from DB Path as shown in the picture..

6. After selecting the DBC file, click the checkbox "View in CANbus Overview" in the Message Overview section.

Next to OBD PIDs, click the 'View in CAN Overview' checkbox to display the available messages.

This will display all the available messages.

7. In the CAN Overview, select the Engine_RPM and Vehicle_Speed channels (using the checkbox).

In "CAN Overview", select the Engine_RPM and Vehicle_Speed via the checkbox.

8. In the CAN Overview, also set the 'update rate' to "20 Hz" (the fastest request rate for OBDII) and the Interpolation to "Linear". Interpolation smooths out the rpm, otherwise it will have "stair steps" due to the digital nature of the OBD II bus.

Graph of OBDII RPM vs Time Data: Interpolation "Linear" in Green (smooth curve), "Sample and Hold" in red (as from OBDII)

It may be necessary to use the slider bar at the bottom of the CAN bus setup menu and scroll to the right to find the 'Update Rate' field. It is the last column.

9. Press the "Apply" button, and acknowledge the OBDII message.

10. Go to the "Measure" worksheet to acquire data.

How does it compare?

Can the OBDII really replace a tachometer and get accurate results?

Here is a comparison of a physical tachometer installed on an engine with a 1 pulse per revolution signal (Red curve) with the engine rpm acquired via the OBDII with 20 updates a second and linear interpolation (Green curve).

Questions? Email peter.schaldenbrand@siemens.com or contact Siemens Support Center.

More Simcenter Testlab Acquisition Tips:

Simcenter Testlab Displays

KB Article ID# KB000038714_EN_US

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Associated Components

SCADAS Durability SCADAS III SCADAS Lab SCADAS Mobile SCADAS PBN SCADAS RS Configuration App SCADAS RS Hardware SCADAS RS Recorder App SCADAS Recorder SCADAS XS