FAQs

FAQs for the SmartSens family

Can PNI's sensors be used to build detection devices?
Yes. PNI's magneto-inductive sensors have been used in a number of detection applications; some of the most common being the detection of a car passing by a specific area. Our sensors have also been used in applications where objects from as small as a bullet to as large as an ocean going ship have needed to be detected.

How is a magneto-inductive (MI) sensor different from a fluxgate?
To measure a magnetic field, a fluxgate needs to be driven into and out of saturation whereas PNI’s magneto-inductive sensor serves as the inductive element in a low-power L/R relaxation oscillator. This oscillator has an output that is directly proportional to the strength of the measured magnetic field. Since there is no need to drive the magneto-inductive sensor into and out of saturation the circuit design is far less complicated and the power consumption is greatly reduced. The inherently digital nature of the output signal has the additional benefit of removing the need for complex and costly signal conditioning and analog-to-digital circuitry.

How is a magneto-inductive (MI) sensor different from a magneto-resistive (MR) sensor?
Much like a fluxgate, a magneto-resistive sensor requires a much more complex interference circuit than PNI’s magneto-inductive sensor. Power draw also becomes an issue, especially when the system is intended to operate for extended periods on battery power. A typical MR sensor implementation requires 3 volts minimum with a current draw of 6.2 mA minimum as well as 600 mA current pulses for reset at least once per second during use, and once per reading minimum. A typical PNI magneto-inductive circuit operates at 3 volts standard with 2.2 volts available and 1.8 volts possible. With a current draw as low as 0.5 mA, the PNI magneto-inductive sensor solution is well suited for ultra low power applications. Another important difference between magneto-resistive and magneto-inductive sensor technology is their dynamic range. PNI’s MI sensors have a dynamic range that is approximately 100 times greater than that of the magneto-resistive sensors. This increased range allows for the ability to calibrate out large magnetic distortions and gives the MI sensor much better resolution over a greater range of operating conditions.

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 and on the type of battery used. It is recommended that the sensors be mounted as far away from the batteries as possible. As to the types of batteries, Lithium has the least magnetic signature, followed by Alkaline, with NiCad (Nickel-Cadmium) having the highest magnetic signature. Also, be careful when using any type of rechargeable battery, as they tend to change characteristics during discharge and after each charging cycle.

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 the motors as possible, but if that is not possible then shielding the motor may help to reduce the distortion levels. Unfortunately, shielding the motor may cause a soft-iron distortion due to the 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 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 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.