Replacing a Speed Sensor is Not Easy
Magnetic field sensors are commonly used for non-contact speed, count, or position measurement. Replacing a sensor for a specific application can be difficult. Our Hall Effect magnetic field sensors are designed using a modular manufacturing concept. This allows us to put the same sensor functions into a wide variety of packages with the shortest lead-times in the industry. Currently over 6,000 unique sensors are available in our catalog. This application note specifically discusses Hall Effect and other sensors used to measure speed and provides guidance in selecting the appropriate options for your application when searching for a replacement speed sensor.
Need Assistance? If you would like assistance in selecting a sensor, contact us to discuss the details of your application.
Determining the Sensor Type and Characteristics
To determine the type of sensor you need, first you need to know what type of target the sensor is detecting. Most sensors produce one pulse per every tooth of a gear, hole in a tone ring, or magnetic pole that passes the sensor face. The target will define the type and characteristics of the sensor required.
Ferrous Targets
Gear teeth, slots in ferrous wheels, ferrous bolt heads, etc.
- VR Sensors (Variable Reluctance) – This sensor type detects any ferrous discontinuity, teeth, holes, bolt heads, etc. without the sensor requiring power. They typically have 2 wires (or a 2-pin connector) and may have a pole piece sticking out of the face.
- Single Channel Gear Tooth Sensors – This sensor type is the best choice for detecting standard, evenly spaced gear teeth, and are Active true zero Hall Effect speed sensors.
- Target Tracker Single Channel Gear Tooth Sensors – This sensor type is the best choice for detecting unevenly spaced teeth on gears along with other ferrous discontinuities like bolt-heads or widely spaced holes.
Magnetic Targets
One or more rare earth magnets or magnetic fields.
- Hall Switch Sensors
- Magnets have at least 1 North and 1 South Pole. There are multiple types of Hall Switch options.
- South Pole detection is the most common; Either Pole and North Pole only options are also available.
- Some magnets produce very little field, so they need a very sensitive Hall (or MR) Switch.
- Some magnets produce a large field, and will triple-trigger a sensor that is too sensitive.
- Some magnets have multiple-pole pairs and will produce multiple output pulses from a passing magnet.
- Hall Latch Sensors – These sensors are active Hall Effect sensors whose output switches when one magnetic pole is introduced but holds that output until the opposite pole is introduced. These sensors would produce 8 pulses on a 16-pole magnet.
Resolution/Scaling
A replacement sensor needs to produce the same number of pulses per revolution as the existing sensor.
If the old sensor provided 8 pulses per rotation from a 16-pole magnet wheel and you replace it with an either Pole Hall switch that produces 16 pulses, your reading will be twice what is expected. If you are changing your target or sensor type, be sure to either match the number of targets as the original or change the scaling in the controller.
Jump to: Determining the Sensor Type and Characteristics | Selecting Sensor Attributes | Functional Features | Electrical Features | Output Type | Supply Voltage | Housing | Connection
Selecting Sensor Attributes
Once you have determined the type of sensor, you can narrow down the product line by selecting attributes. Below we have listed the attribute types and what they mean. When narrowing down sensor selections start with the attributes that are most important to your application.
Need Assistance? If you do not find the selection you want from the attributes, contact our Engineering Department to discuss alternative options to those listed in our catalog. In many cases we can provide a new solution with existing materials.
Functional Features
Functional Features will narrow down sensors within a category by specific features, regarding speed selection they may indicate whether the sensor is providing digital pulses versus a sine wave output, or if sensors are better for coarse vs. fine target pitches (gear tooth sensors), sensitivity (Hall Switches), or other features that will be specific to the type of sensor.
Jump to: Determining the Sensor Type and Characteristics | Selecting Sensor Attributes | Functional Features | Electrical Features | Output Type | Supply Voltage | Housing | Connection
Electrical Features
Electrical Features are related to the power supply or outputs, common electrical features are detailed below
- Internal Pull Up or Pull Down Resistors – Our magnetic speed sensors are commonly offered with 5K internal pull ups to be compatible with 5-24V power sources, most controllers work fine with a wide range of different pull up resistors. Sensors can be built with larger or smaller pull up values if required, contact our Engineering department to discuss requirements for your specific application.
- Open Collector Output – These sensors expect a pull up resistor to be built into the controller that is reading the sensor. Sometimes even if the controller is expecting an open collector and you use a sensor with an internal pull up, the pull up values are in parallel and the signal is the same. Other times, the sensor is powered with 12 volts and the internal pull up resistor is pulled up to 5 volts; adding an external pull up resistor to the sensor may blow up the controller.
- EMI Filters and Load Dump Protection – These options include additional protective circuitry for applications where EMI interference, or power stability issues may be a concern such as automotive and equipment applications powered by 12V and 24V batteries. These options can be applied to sensors with and without internal pull up resistors.
Jump to: Determining the Sensor Type and Characteristics | Selecting Sensor Attributes | Functional Features | Electrical Features | Output Type | Supply Voltage | Housing | Connection
Output Type
Combined with producing the correct number of pulses, a replacement sensor has to work with the same supply voltage and produce the same output as the existing sensor. Dependent on the sensor type required there will be multiple options.
NPN Output
These current sinking sensors provide square wave outputs that switch between 0V and the supply voltage. These sensors typically have the output pulled to the high state with no target present and then output switches low when the target is present. The output is either pulled to the high state by a resistor within the sensor, or the pull up may be in the controller.
Sine Wave Output
VR sensors produce a sine wave for every ferrous tooth that passes the sensor face. These sensors do not require power. The sine wave is very low amplitude peak to peak at slow speeds. This amplitude increases with speed. There are hundreds of different electrical variations of VR sensors, some designed for fine teeth and some designed for larger teeth. In general, if you get enough amplitude, you will trigger the controller that reads the signal. Since the amplitude increases with speed, you need to make sure your maximum signal peak to peak does not blow up the controller that reads the signal.
PNP Output
These current sourcing sensors provide square wave outputs that switch between 0V and the supply voltage. These sensors typically have the output pulled down to the low state with no target present and then output switches high when the target is present. The output is either pulled to the low state by a resistor within the sensor, or the pull down may be in the controller.
Relay Output
Reed Switch Sensors and some Hall Switches provide an output that opens or closes a relay dependent on the presence or absence of a target magnetic field. The relay switching can be counted by some controllers for resolving speed.
TTL Output
TTL Type outputs will provide 0-5V digital square waves regardless of if the sensor is powered with 5V, 12V, or 24V.
Jump to: Determining the Sensor Type and Characteristics | Selecting Sensor Attributes | Functional Features | Electrical Features | Output Type | Supply Voltage | Housing | Connection
Supply Voltage
When narrowing options by the Supply Voltage to be provided to the sensor, be sure to check all boxes where your supply voltage fits in that range. Upper and lower limits of supply voltage are dependent on the sensing element as well as circuit protection and regulators that may be found within the sensor.
Jump to: Determining the Sensor Type and Characteristics | Selecting Sensor Attributes | Functional Features | Electrical Features | Output Type | Supply Voltage | Housing | Connection
Housing Material
Our Hall Effect sensors are offered primarily in Stainless Steel, Anodized Aluminum, and molded plastics. If your application has a specific material requirement or grade of steel contact our Engineering department to discuss requirements for your specific application.
- Mount Type – Sensors are available in threaded packages with lock nuts for mounting into brackets or threaded ports. These are referred to as “Threaded Barrel” housings. They are also available in packages where one or more bolts mount into a flange to position the sensor and in smooth cylinders (referred to as smooth barrel).
- Thread Pitch – For applications where the diameter or specific pitch of threads is critical, Standex Detect offers threaded barrel housings in a wide variety of pitches. You can select one or more thread pitches to narrow down selections for your application.
- Housing Length in Inches – In this attribute you can either select specific housing lengths or use the min and or max fields to define upper or lower limits to the length of the housing. This length is the distance from the sensing face to where the connection exits the sensor. Integral connectors do increase the length of the sensor.
Jump to: Determining the Sensor Type and Characteristics | Selecting Sensor Attributes | Functional Features | Electrical Features | Output Type | Supply Voltage | Housing | Connection
Connection Type
We offer 6 categories of connection types listed below.
- Free End Wires – Free end wire connections will have individual insulated wires exiting the sensor. These are typically low-cost connections, and they also allow power and ground to be wired to a power supply and the output(s) to be wired to a meter or controller without jumper wires.
- Ribbon Cables – Ribbon cables are bonded free end wires. They are also a low-cost solution for a connection type but remain together unless pulled apart during or after installation. Currently only 3 conductor ribbon cable options are offered.
- Jacketed Cables – Jacketed cable connections will have all the sensor wires enclosed in an outer jacket. The sensors will be provided with a couple inches of this jacket removed at the end of the cable.
- Shielded Cables – Shielded cable connections are like jacketed cables but also have a shield around the wiring to protect the signals from external interference. These cables will either have a foil shield or a braided shield along with a drain wire. Note: The shield is not tied the to the sensor housing during assembly.
- Integral Connections – We offer many sensor types with options to have M12 circular connectors, MS style connectors, and other options integrated directly into the back of the sensor housing. The advantage of integral connections is that it allows the sensor (or wiring harness) to be individually replaced instead of needing to re-run the cable if the sensor is damaged or replace the sensor if the cable only is damaged.
- Pigtail Connections – Pigtail connectors are available with a wide variety of options including Deutsch DT Series Connectors, Paccard Connectors, Amphenol Connectors, MS Style Connectors, M12 circular connectors, and other specialty options. Standard pigtails have defined lengths and wire types. Custom pigtails can also be designed to meet the specific requirements of the application.
Wire Gauge
If the application requires a specific size of wire, it can be selected here. Note: Most magnetic field sensors use very little power and are running on low voltage systems. 26AWG wires are more than adequate to handle power consumption of most sensors.
Connection Length
Connection lengths are sorted in categories. If the connection length required for your application is not available contact our Engineering department to discuss the specific requirements of your application.
Insulation Material
The insulation material typically determines the temperature range and durability of the cable. For jacketed and shielded cables, the listed insulation material is for the outer jacket. The inner conductors may have the same or different insulation materials.
Application Notes
Sensor Selection Application Notes
Custom Speed Sensors & Direction Dependent Speed Switches
Custom Magnetic Sensor Design and Manufacturing
Guide to Replacing a Speed Sensor
Selecting the Appropriate Hall Effect Sensor and Target Magnet
Why do I need to provide the gear pitch when ordering a Speed and Direction Gear Tooth Sensor?
Target Selection Application Notes
Selection or Design of Sensor Targets
Selecting the Appropriate Hall Effect Sensor and Target Magnet
Sensor Behavior Application Notes
Chopper Stabilization and Gear Tooth Sensors
The Effect of Mounting A Ferrous Metal Sensor in a Steel Sleeve
Understanding Duty Cycle and Phase Angle in Quadrature Sensors
Why Either Pole Hall Switches May Produce 3 Pulses from a Single Magnet
Sensor Output Monitoring Application Notes
How to Hook Up an LED to a Magnetic Sensor
Understanding Duty Cycle and Phase Angle in Quadrature Sensors
Meters and Signal Conditioners
How To Hook Up a Digital Magnetic Sensor to a Relay
Custom Hall Sensor Application Notes
PCBA Manufacturing & Design – Printed Circuit Board Prototyping Services
Thief Hatch Latch Detection Systems
If the sensor characteristic or target magnet you are looking for is not located in this document, contact our Engineering Department to discuss your specific requirements.
Click here to return the Hall Effect Application Notes page