Pressure and Other Sensors

Pressure Sensors  

Customers sometimes require pressure sensors that can be directly powered from +12 volt automotive electrical systems and are compatible with the 0-5 volt analog inputs on our products. SSI Technologies offers a range of cost effective sensors in their P51 series, available from Digi-Key at www.digikey.com. Absolute pressure sensors are recommnded for most applications and required for manifold pressure. The part numbers listed below have 1/8" NPT male fiitings except as noted. Additional part numbers are available. Detailed data sheets with scale factors may be downloaded from the SSI Technologies website at www.ssitechnologies.com.

Typical SSI P51 Series Pressure Sensor

Part Number Pressure Range Notes
P51-15-A-UB-I36-5V-000-000 0-15 PSIA Manifold pressure - normally aspirated
P51-50-A-B-I36-5V-000-000 0-50 PSIA Manifold pressure - boosted
P51-100-A-B-I36-5V-000-000 0-100 PSIA  

P51-200-G-B-I36-5V-000-000

0-200 PSIG  

P51-300-G-B-I36-5V-000-000

0-300 PSIG  
P51-1000-A-B-I36-5V-000-000 0-1000 PSIA  

P51-1500-A-AA-I12-5V-000-000

0-1500 PSIA 7/16-20 UNF male fitting

P51-3000-A-AA-I12-5V-000-000

0-3000 PSIA 7/16-20 UNF male fitting

 

Gear Tooth Sensors  

Magnetic gear tooth type sensors are generally used for crankshaft position and vehicle speed sensing. Gear tooth sensors detect the presence of a ferrous (iron) metal target. The sensor contains a biasing magnet. As the ferrous target (i.e. tooth on the crankshaft) passes over the sensor, it affects the local magnetic field. The sensing element detects the change in the magnetic field and generates an output signal. 

Magnetic gear tooth sensors only work with a soft iron target. They cannot detect the presence of non-magnetic materials such as plastic, copper, brass, aluminum, or most stainless steel alloys. They function best when they are mounted in a non-magnetic housing. The typical motorcycle application where the sensor is mounted in an aluminum alloy crankcase and detects teeth on a forged steel crankshaft is an ideal situation for this type of sensor.  

Gear tooth sensors fall into two main categories: variable reluctance and Hall Effect. Both sensor technologies have been widely and successfully applied for many years in the automotive industry. Tradeoffs are summarized in the following table:

 

  Hall Effect Variable Reluctance (VR)
RPM range Zero RPM/speed sensing. Signal level unaffected by RPM. Minimum RPM. Signal level proportional to RPM. Must consider if signal level will trigger ECM under worst case cranking conditions 
Signal output Digital 0-5V square wave Analog sine wave. Peak-peak voltage level proportional to RPM. Requires signal conditioning in ECM. 
Noise immunity High Acceptable
Technology Semiconductor Hall Effect element with built-in signal conditioning Simple coil winding. Most rugged construction possible
Electrical Interface Typically 3-wire (power, signal output, and ground) 2-wire (signal and signal return)
Temperature range -40 to +150C typical. Semiconductor element may fail at higher temperatures  -40 to +150C typical. Usually survives higher temperatures

 

All variable reluctance sensors applications require careful analysis and testing of the worst case signal output under cranking or low speed conditions. This includes consideration of worse case sensor air gap due to manufacturing tolerances, low battery voltage, and cold temperature conditions. Hall Effect sensor are capable of zero-speed sensing and less affected by other conditions that may cause problems. Hall Effect sensors are generally used for vehicle speed sensing.

 

Typical Crankshaft Position Sensors

 

Two typical crankshaft position sensors suitable for motorcycle applications are shown above. The sensor on the left  is the OE H-D P/N 32707-01 used on late model Twin-Cam engines. The part on the right is a Honeywell VR (variable reluctance) sensor. These two parts are used to illustrate general requirements: wire harness pigtail or integral connector, mounting bracket, and O-ring seal. All the suggested sensors have similar constructions and dimensions. Other industrial sensors using screw thread type housings are available, but not suitable for engine applications due to difficulties in sealing threads and setting the correct air gap. 

 

Gear Tooth Sensor Waveforms  

Typical VR and Hall Effect sensor waveforms are shown below. The VR sensor generates a sinewave signal with amplitude proportional to RPM. It does not require an external power source. Minimum signal requirement to trigger the ECM is 1 volt peak-peak with a 2.7K Ohm load on the sensor output. Hall Effect sensors always require an external power supply and pull-up resistor. Hall Effect sensors are capable of zero-speed sensing and the signal output is a square wave with amplitude independent of RPM. 

Proper air gap between the sensor and crank trigger wheel is required. A nominal air gap of .030" is common. You must consider manufacturing tolerances, thermal expansion effects, and run out. For a VR sensor, the signal amplitude will rapidly decrease as the air gap increases. For a Hall Effect sensor, the signal will become erratic and then disappear when a critical air gap is exceeded. You must observe and confirm the signal waveforms. You can visit our Diagnostic Tools Tech FAQ for advice on suggested test equipment.

   

     

Gear Tooth Sensor Waveforms

 

Twin Cam Crankshaft Position Sensor System  

To be compatible with existing engine control modules for Twin Cam applications, the crankshaft position (CKP) sensor system must have 32 teeth (30 actual and 2 missing)  and the same timing relationship as the OE H-D design. We have included a PDF file that shows the required timing relationship.

 Crankshaft Position Sensor Timing Chart

 

Establishing the required timing relationship between the sensor and trigger wheel is a complicated process and some trial and error experimentation will be required. The sensor waveform and timing chart information we have presented above can serve as a starting point. Once the components are mounted on the engine, you can connect a Daytona Twin Tec ECM and use a timing light. When you crank the engine, the ignition should fire at TDC.  

 

Gear Tooth Sensor Suppliers  

The table below lists major suppliers:

Supplier Website
AEC (American Electronic Components) www.aecsensors.com
Cherry www.cherrycorp.com
Delphi www.delphi.com
Diamond www.diamond-us.com
Honeywell www.honeywell.com

SSI (OE supplier for H-D)

www.ssitechnologies.com
Wabash www.wabashtech.com

 

Gear Tooth Sensor Data Sheets and Application Notes  

We have compiled data sheets and application notes for applicable gear tooth sensors from the vendors listed above. The Honeywell application notes (Introduction to VR Sensors and Hall Effect Sensing Chapters 1-7) are particularly useful. The compilation is in the form of a ZIP archive file that you can download by clicking on the link below. You will require PKZIP to unzip the individual files within the archive. If you do not have PKZIP installed on your computer, you can download it from the PKWARE Inc. website.

Gear Tooth Sensor Data Sheets and Application Notes

 

Vehicle Speed Sensor Using Driveshaft Mounted Split Collar Magnet Assembly  

A Hall Effect sensor along with a driveshaft mounted split collar magnet assemebly such as the 800-CL-2M series available from Racepak (www.racepak.com) can be installed on older race vehicles for vehicle speed data logging with Daytona Sensors CD-1, NC-1, NC-2, SL-1, and TC-1 systems. The Racepak split collar magnet assembly is typically installed on the rear yoke or coupler and is available in a wide range of standard and custom sizes. 

Unlike the gear tooth sensors described above, this application does not require a special Hall Effect sensor with biasing magnet. A Honeywell P/N SR3F-A1 unipolar Hall Effect sensor available from Digi-Key (www.digikey.com) can be connected as shown below.  The 4.7K ohm pull up resistor provides a 0-12V square wave signal. 

 

Vehicle Speed Sensor Hookup

Daytona Sensors P/N 116003 vehicle speed sensor harness, shown below, includes the Honeywell sensor and 4.7K resistor. Additional details, including a formula to calculate the VSS frequency based on gear ratio and tire OD, are available in the Vehicle Speed Sensor Tech Note.

Daytona Sensors P/N 116003 Vehicle Speed Sensor Harness and Typical Magnet Collar (Not Included)