FAQs

FAQs for the CompassPoint family

Do I need to re-calibrate when I change locations?
No, re-calibration is not necessary. Compassing is ratiometric, so when the total field strength changes the sensors change proportionately and the heading will still calculate correctly.

How can I determine the heading errors associated with tilt when using a 2-axis compass?
By using the following formula you can get a general idea of the amount of error you can expect for a given amount of tilt at the location on earth that you will be taking the measurement. You will need to go to the National Geophysical Data Center site to determine the magnetic values (V and H) needed for your area.

  • Heading Angle = θ
  • θ = arctan (Y/X)
  • Heading Error: θ = arctan ( V*sin (degrees of tilt) / H )
  • V = the vertical magnetic field component
  • H = the horizontal magnetic field component

How often do I need to calibrate my compass?
Typically the need for recalibration is due to system changes, the compass itself can go years without needing re-calibration. If the system changes magnetically the compass would need a new user-calibration. System changes which would require re-calibration include becoming magnetized, swapping out ferrous components if they are not magnetically the same or re-locating components.

My application is battery powered. Will the batteries have any effect on the sensors performance?
That depends on the location of the battery relative to the sensors, the type of battery used, and the PNI product being used. For instance, PNI's CompassPoint and FieldForce family of products incorporate PNI's proprietary hard and soft-iron correction algorithms which compensate for the magnetic distortion effects introduced by batteries. Still, it is recommended the sensors be mounted as far away from batteries as possible. This is especially true when using any type of rechargeable battery, as they tend to change characteristics during discharge and after each charging cycle. As to the types of batteries, Lithium has the least magnetic signature, followed by Alkaline, with NiCad (Nickel-Cadmium) having the highest magnetic signature.

The TCM2 had analog output available, do any of the current products offer this?
No unfortunately they do not.

The area I want to mount the sensors/module is near a motor, is that going to be a problem?
Since electric motors usually generate magnetic fields that are much stronger than the earth’s field, being in close proximity to the sensors could cause a hard-iron type distortion. It is recommended that the sensors be moved as far away from any motors as possible, but if that is not possible then shielding a motor may help reduce the distortion. Unfortunately, shielding the motor also may cause a soft-iron distortion due to the shielding materials used. Trial and error may be needed to find a location and/or shielding method that will work best in your application.

What are hard-iron and soft-iron magnetic distortions?
PNI's compass modules compensate for hard-iron and soft-iron magnetic distortions. Brief explanations of hard-iron and soft-iron distortions are given below, and a more detailed explanation is provided in PNI's white paper "Magnetic Distortion Explanation & Testing". Hard-iron distortions are caused by permanent magnets and magnetized ferrous materials within close proximity to the sensors. This type of distortion is of constant magnitude and in a fixed location relative to the sensors for all heading orientations. Hard-iron distortions add a constant magnitude field component along each axis of sensor output and can be compensated for by using a simple subtraction method. Soft-iron distortions are the result of interactions between Earth’s magnetic field and any magnetically “soft” material within close proximity to the sensors. In technical terms, soft materials have high permeability. The permeability of a given material is a measure of how well it serves as a path for magnetic lines of force, relative to air, which has an assigned permeability of one. Soft-iron distortions result in varying field strengths depending on orientation and are considerably more difficult to correct than hard-iron distortions.

What is a PNI digital compass?
PNI digital compasses incorporate a patented magnetic sensing technology, called magneto-inductive sensing. It electronically senses the difference in Earth's field from your system's magnetic field, then an on-board microprocessor electronically subtracts out your system's magnetic fields, reporting highly accurate compass readings. Magneto-Inductive sensor technology has many advantages over other technologies, including high resolution, superior linearity and repeatability, and reduced power consumption. These advantages have made magneto-inductive sensor technology the choice for many high-profile compass applications including GM, Ford, and DaimlerChrysler automobiles, Polaris jet skis, Bayliner boats and Timex watches.

What is the difference between a 2-axis compass (ex. Vector 2Xe) and a 3-axis compass (ex. Prime or TCM)?
A 2-axis compass uses 2 magnetic sensors placed at a right angle to each other with the sensing axes level with respect to gravity. A compass made this way determines heading by a simple arctan function of the output of each sensor and is accurate only when held to a level orientation. Once the compass is tilted heading errors will occur that will vary depending on the location on earth the compass is at the time. A 3-axis compass uses 3 magnetic sensor mounted orthogonally and a tilt sensor to determine the gravity vector. This type of compass, when properly calibrated, will use the input of all the sensors to determine accurate heading regardless of the tilt applied, within the range of the tilt sensor. PNI produces both 2-axis and 3-axis compass modules and the sensors needed to implement your own solution.

What is the difference between magnetic north and true north?
In most places on earth, true or map north is not the same location as magnetic north. This is because the magnetic fields of earth are always slowly changing. If you want to find the exact difference (called declination) between magnetic and true north in your area, contact the National Geophysical Data Center in Boulder, Colorado, where you can get a declination based on the latitude and longitude of your location. To find out your latitude and longitude in the US, go to the US Census Bureau web page that supplies them based on city and state or zip code

What is the purpose of the CommBoard and how do you communicate with it?
The CommBoard provides a quick and easy way to make a connection between a computer and a PNI V2Xe or MicroMag module. It is intended as a user development and evaluation tool, such that a module can be installed and running in a matter of minutes. It supports RS232 and RS485 using either PNI application software or a terminal emulation program such as Hyperterminal.

Why is calibration necessary?
Calibration is the process used with PNI sensor technology to separate the earth's magnetic field from magnetic field distortions created by the environment into which the sensors are mounted. An example of this would be the hard-iron magnetic distortions created by the engine and body of a car. By implementing a simple calibration routine with the sensors in a fixed position within the car, the maximum and minimum field strengths can be determined and then used to correct the sensor output for the distortions present.