ABS Testing Application Note

General

The Thermotron Product Test System (PTS) has been applied to Anti-Lock Brake System (ABS) controller testing. This application note will give you some ideas on how this testing can be accomplished. The PTS required to implement an ABS tester has a low cost, is modular, flexible and includes the ability to run multiple tests on multiple products.

Typical ABS Controller Product

For a ABS controller to operate, it must receive power, signals representing wheel motion sensors, correct loads and control signals. An ABS controller will typically output signals which control valves and warning lights. When wheel slippage is detected from the input wheel motion sensors, corresponding outputs are activated.

General Testing Strategy

ABS controllers may be tested in several modes. This application note details testing that simulates normal operation. Another form of testing, not described in this application note, involves "downloading" test programs into the ABS module. Both modes of testing can be accomplished with a single PTS system. A general functional block diagram of an ABS controller tester is shown in Figure 1.

Providing ABS Controller Power

Power supplies, under control of the PTS, can provide a programmable power source capability for ABS controllers to be tested. This capability includes the ability to stress the product with lower and higher than normal operating voltages. To control a power supply, a Power Supply Programming Module (PSM-2) function module is utilized. The PSM-2 is capable of controlling 2 independent power supplies with resistance programming.

Providing ABS Controller Stimulus

Several control signals, such as ignition, are typically supplied to an ABS controller. These signals can be controlled via a PTS Digital Waveform Generator (DWG-08).

To provide the signals that simulate the wheel sensors, a more elaborate scheme is required. The PTS Analog Waveform Generator (AWG-04) is capable of generating any arbitrary waveform. To produce a combination of stable and sweeping frequencies an additional summing amplifier could be used. With this configuration (Figure 2), any combination of wheel motion can be simulated.

If the ABS controller is expecting to receive a signal representing a brake pump motor, a AWG-04 could be used for this purpose also.

A function module such as the Automotive Bus Module (ABM-05) would be utilized if the ABS controller has serial communications capability. This capability can be utilized to download test programs or read out diagnostic data.

Sensing ABS Outputs

Proper operation of the ABS controller warning lamp, and other miscellaneous outputs, could be sensed with an Analog Input Module (AIM-32). A combination of a High Frequency Multiplexer (HFM-08) and a Digital Waveform Analyzer (DWA-04) would allow a complete analysis of brake valve voltage and current.

Load Boards

Load boards provide an interface between the PTS and the product(s). Additionally, load boards provide simulated loads, a convenient location for test points, diagnostic displays and configuration jumpers. For example, a load board could provide loads that electrically resemble the brake valve actuators. If the product is connected to these loads through relay contacts, the PTS could test the products response to an open or shorted load.

PTS Profiles

Once the PTS equipment is set up, the PTS software must be configured. To configure the PTS software, profiles are defined for the function modules that are used. No programming is required. It is important to have a clearly defined idea as to the signal requirements for product stimulus, the product output signals, and the PTS to product configuration. For example, profiles may be created for the AWG-04 that causes a simulation of a wheel slip condition. A DWA-04 profile may then be created to check for proper brake valve actuation.

Possible ABS Controller Tester Physical Configuration

A 19 inch console is typically used for PTS equipment mounting. AC power is normally distributed with an outlet strip and excess heat is dissipated with a blower located at the top of the console. Casters on the bottom of the console will contribute to convenience. Figure 3 illustrates a possible PTS configuration.

Load boards are typically located toward the top of the console and the PTS base unit is located toward the bottom, near the power supply. The PTS PC is typically located at a height that allows for easy operator access.

Connections between the PTS console and the products can be accomplished via cables that connect to the back of the PTS cabinet. These cables can connect directly to the air bag controllers, or to replaceable adapters. Note that is often desirable to locate PTS and product connections inside the console (as opposed to the front of the console). This increases the cabling protection, limits cable lengths and reduces the chance of tampering.

Conclusions

This application note demonstrates the possibility of creating a capable, cost effective, flexible method of testing air bag controllers with the Thermotron Industries PTS. This testing can be done in either production or laboratory environments. Contact Thermotron to have your testing needs analyzed and solved.