Sensor Ratiometric Correction

Overview

A sensor’s analog output is always proportional (ratiometric) to its supply voltage. The lower the supply voltage, the lower the sensor output voltage. The ECU can correct for this variation in supply voltage and improve sensor performance by applying a ratiometric correction; this is a ratio of the actual sensor supply to the calibrated/ideal sensor supply (5.0V). To do this the ECU must know what supply has been wired to the sensor. There are currently 4 options:

1. OFF — ECU applies no sensor ratiometric correction
2. ECU 5V Ref — Pin D21 on a KV Series ECU OR Pin B2 on SL series ECU
3. ECU 5V Ref2 — Pin D22 on a KV Series ECU
4. 5V Ref Ext Supply

The sensor reference supply can be selected from Emtune by opening the Setup panel of a selected Input Channel.

5V Ref Ext Supply

Some sensors may be supplied from an external voltage/supply source. For the ECU to apply ratiometric correction to such a sensor, the ECU needs to know this voltage, so it must be wired into the ECU for measurement. Set up as follows:

1. Connect to the ECU with Emtune. Config View → Channels → Calculated Runtime → Main. Select the “5V Ref Ext Supply” setting and pick an input source from the list.

2. This runtime can now be viewed from the Runtime menu (F3) → ECU Internal tab. This runtime will be used for the “5V Ref Ext Supply” ratiometric correction, so it must accurately represent the sensor supply voltage.

Example

The following test was completed using a 3.0-Bar MAP sensor operating at barometric pressure. A comparison is shown in Table 1.0 between the Ratiometric Correction OFF and ON. With the Ratiometric Correction ON the ECU is able to generate a consistent output for variations in the sensor supply voltage.

Table 1.0 — MAP Sensor output, Ratiometric OFF/ON Comparison

Aux Output Notes

Emtron ECU systems have a high number auxiliary outputs on all products offered in addition to being able to utilize unused fuel and ignition channels as additional outputs. These extra outputs can be used for various functions such as solenoid control, relay control (fans, fuel pumps, etc), PWM systems, and more. Keeping with the concept of Emtron flexibility, the Aux Outputs match these needs.

Regardless of this added flexibility, careful planning for best output use is still necessary.

Aux Output Connections

SL Series ECU – 10 Aux Outputs

Auxiliary 1-4: Low side

Outputs rest at 0V when ECU is powered off

Outputs are open when not being commanded on

    Low side control of relays, solenoids, lights, etc

Auxiliary 5-8: High side/Low side

Outputs rest at 0V when ECU is powered off

Outputs are open when not being commanded on regardless of polarity

    Low side or high side control of relays, solenoids, lights, etc 

Auxiliary 9-10: Half bridge (DC motor control – DBW)

Outputs rest at 0V when ECU is off 

Outputs command the opposite polarity when off

    IE – High side output as commanded on is low side when off

KV Series ECU – 16 Aux Outputs

Auxiliary 1-8: High side/Low side

Outputs rest at 0V when ECU is powered off

Outputs are open when not being commanded on/off regardless of polarity

    Low side or high side control of relays, solenoids, lights, etc 

Auxiliary 9-16: Half bridge (DC motor control – DBW – Aux 9-12 KV8 ONLY)

Outputs rest at 0V when ECU is off

Outputs command the opposite polarity when off

            IE – High side output as commanded on is low side when off

** KV8 Aux 13-16 cannot be used as DBW control, but the functionality regarding output state is the same

Common Issues

When using an Aux Output to control a low side output that is connected to constant power.

The result is the output is ON when the ECU is powered off.

See KV Series Hardware Manual - Section 3.6

This is why the control side of many systems (relays, solenoids, etc) is switched on with ignition supply (OEM).

Due to the flexibility of the output, controlling the system as High Side instead can resolve this issue.

When using a Half Bridge output on a circuit that is sensitive to reverse polarity, this can create issues with actuation if that particular output is expecting an open circuit when commanded off.

**** For output specifications (frequency, PWM, current ratings), see ECU specification sheets.**

Closed Loop and PID

The function “Closed Loop” is defined as a control system’s ability to react automatically based on a form of feedback (position, calculated value, frequency, etc).

This is usually dependent on some sort of PID strategy.

The Emtron ECU has closed loop controls for many Functions throughout the ECU.

Common functions that rely on closed loop are:

Closed Loop Lambda Control

Idle speed control

Idle Ignition Control

VVT Cam control

DBW Control

Boost Control

Launch Control - Torque Limiting

Traction Control

All Emtron PID configurations can be very comprehensive. .

Proportional Gain: controls how aggressive instantaneous correction is based on the current target error.

Correction based on proportional error

Example 1 -

Boost Target Error = 10%

P Gain Table Entry = 1.0

P Gain Correction = 10% * 1.0 = 10%

Example 2 -

Boost Target Error = 10%

P Gain Table Entry = 2.0

P Gain Correction = 10% * 2.0 = 20%

Integral gain: controls how much adaptive correction is needed over time after the application of proportional control.

The Integral Gain will multiply the gain value vs the target error at the control rate speed.

Derivative gain: controls predictive correction. It is based on the rate of change of the error.

The target error rate of change will multiply vs the Derivative gain.

A delicate balance of these values is normally needed to provide accurate and precise control of the closed loop system.

To provide more accurate closed loop control, Emtron allows values can be spanned in 3D to allow a look up table to actively adjust based on whatever runtime is desired.

This allows the user to fine tune the closed loop functions without just relying on the target error solely.

Feed forward functions

The feed forward value allows the PID function to operate with greater accuracy if drive duty can be predicted.

Min/Max limits

These are used to clamp the PID functional range if necessary.

Enumerations

• Active Center Differential
• Boost Status
• Closed Loop Fuel Status
• DBW PID Status
• DBW System Status
• Engine Protection Status
• Highest Priority Fuel/Ign Cut Status
• ORFC Status
• Traction Control Status
• VVT System Status

Fault Modes & DTC Codes

The ECU monitors the relationship between the Servo Positions 1/2 signals, Pedal Positions 1/2 signals and Target vs Actual Plate Position. When an error occurs the ECU will generate the following DTC’s

• P1574 Throttle Position Sensor Disagreement between Sensors
• P1577 Pedal Position Sensor Disagreement between Sensors
• P1570 DBW Target Tracking Error
• P1581 DBW Shutdown

The DTC code will be cleared automatically by the ECU when the fault condition is removed. However, an error counter will be incremented so the fault history can be viewed.

During an active DBW DTC the ECU will limit the engine speed for safety reasons. There are several options available using the DBW Fault Mode setting:

1. Non adjustable engine limit set at 2000RPM.(Recommended setting)
2. Use Limp Home Table1. This is an adjustable 3D table.
3. Use Limp Home Table2. This is an adjustable 3D table.

Wiring References

• V7-V9 & H6 ISC Pinout - Subaru
• Bipolar Stepper Motor Pinout - Delco
• LS1 DBW Throttle Body Pinout
• LSU 4.9 Pinout
• Magnetic-Resistive Sensor Wiring