FAQs

FAQs for the CompassPoint family

FAQs for the V2Xe

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

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 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 Hard-iron and Soft-iron?
Hard-iron distortions are caused by permanent magnets and magnetized steel or iron object within close proximity to the sensors. This type of distortion will remain constant and in fixed location relative to the sensors for all heading orientations. Hard-iron distortions will add a constant magnitude field component along each axis of sensor output and can be easily compensated for using a simple subtraction method. Soft-iron distortions are the result of interactions between the earth’s magnetic field and any magnetically “soft” material within close proximity to the sensors. In technical terms, soft materials have a 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. The V2Xe 2-axis digital compass, as well as PNI’s high performance 3-axis instruments, feature soft- iron and hard-iron correction.

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

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.

Can I connect the V2Xe to a processor operating at 5V?
No, a level shifter should be used between the V2Xe and 5V processor.

Can I run the V2Xe at 5V?
No, the V2Xe is designed for 3V operation with 4.1V maximum.

Does the period select need to be calibrated at the same setting it will be used at?
No, but it is better that the calibration is done at a higher or equal resolution (period select) than it will be operated at.

How do I enable continuous sampling mode?
Change the “SampleFreq” Configuration parameter to a value greater than 0, then start by sending GetData command. When “SampleFreq” is set to 0, the GetData command returns only 1 sample.

How sensitive are your sensors
The distance of the object from the magnetic sensor will depend on what you want to measure and how accurately. The sensors are very sensitive so can pick up small changes in the magnetic field such as the earth field. However, the closer you are the better it will measure small changes or movements of that object. The sensors do have a certain range of measurement so; you need to make sure the object doesn't saturate the sensors. The best way to determine the desired distance is to first mount 3 sensors in X, Y, Z axis and make some measurements.

Regarding the question on how much surface exposure… Well magnetic fields are vectors which means it has direction and amplitude. There is no minimum surface exposure needed as long as the axis of measurement is not perpendicular to the sensor. To measure the magnetic field we recommend the use of 3 sensors oriented 90 degrees apart. This will ensure that all magnetic field vectors are measurable.

I calibrate the V2Xe and still get -1 out for heading, what is wrong?
The module rejected the calibration as being of poor quality.

I get a heading output of -1 what does this mean?
A heading of -1 means that the compass has not yet been calibrated. ($C-1x0y0…..)

My CommBoard will not read the Z-axis even when in RAW mode, what is wrong?
Your Commboard may have old firmware which does not support a z-axis. Z-axis support was added with firmware V207.

My module is a magnetometer only module yet I get heading output from the CommBoard, how come?
The CommBoard has a controller with loaded algorithms for calculating heading from a 2-axis magnetometer system. Even though the module does not have this capability alone it gives the user additional evaluation tools reflecting what can be developed in the final application.

The middle two LEDs don’t ever turn ON, what are they for?
These are for future use and have not been designated a purpose yet.

What application can be used to communicate to the CommBoard?
The CommBoard can be communicated with using the PNI application software or a terminal application such as Hyperterminal.

What are valid SampleFreq values and what do they represent?
Whole numbers from 0 to 8 are valid SampleFreq settings with numbers 1 – 8 representing the output in Hz and 0 is single sample setting.

What conditions would result in a poor quality calibration?
Performing the calibration near a transient distortion. This could be passing over a ferrous object or being too close (<3 feet) to a CRT screen. Also if the period select is too low it will not have the resolution for a good calibration.

What interface does the CommBoard support?
The CommBoard supports both RS232 and RS485, jumper selectable.

What is the advantage of using a CommBoard?
The CommBoard allows rapid evaluation of the plug in modules, modules can be installed and running in a matter of minutes.

What is the button for?
The button is a reset and will re-boot the CommBoard

What is the purpose of the CommBoard?
The CommBoard provides a quick and easy way to make a connection between a PNI module and computer. It was designed as a user development and evaluation tool.

What resolution (Period Select) should the V2Xe be set for during calibration?
The V2Xe should be set for a period select of 5 (/512 ratio) or higher during calibration.

When using the CommBoard I get a heading output of -1, what does this mean?
As a default output heading is set to -1 until the unit has been calibrated to prevent modules from being used un-calibrated, giving inaccurate heading information.

Which modules can be used with the CommBoard?
The modules which are supported by the CommBoard are: V2Xe, Micromag2 on Carrier board, Micromag3, MS2100 on Carrier board.

Why doesn’t my Micromag3 give tilt compensated compass heading out of the CommBoard?
A 3-axis compass can’t be implemented without tilt compensation; a tilt sensor is required to perform this function in addition to the magnetometers. For evaluation purposes the CommBoard can use the Micromag3 in two modes, as a 2-axis compass ignoring the z-axis sensor or as a 3 axis magnetometer in raw mode.