FAQs

FAQs for the SmartSens family

FAQs for the MS2100

After sending a command byte can SSNOT be brought high while waiting for DRDY to go high and then taken low to read the sample data? From a big picture view, can I issue a command to the 11096 ASIC, and then use the SPI bus to talk to another device and finally come back to the 11096 ASIC to get the result of the previous command?
Yes, the SSNOT can be brought back high and the SPI bus used to talk to another device.

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.

Can I use the Micromag at 5V?
Yes, it can be plugged in and used at 5V without any changes however it is tuned for 3V. Changing the bias resistors will have better performance but it not required.

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.

Can the ASIC be used with only one sensor?
Yes, the ASIC can be used with any combination from one to three sensors with any axis combination as well.

Does the Micromag3 have pitch and roll outputs?
No, the Micromag3 is a 3-axis magnetometer only.

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 can I test if the sensor is working properly?
The Magnetic Oscillator Test (MOT) can be used which will turn on the sensor chosen and have it run continuously in the direction chosen by ODIR until a rest is done. Command 0000x1xx in binary, where the first x selects oscillation direction and the last two select axis. The sensor can then be probed using an oscilloscope. (I normally don’t use this test but rather just take a sensor sample and review communication waveforms)

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 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.

How is the value of Rb (bias resistor) determined for voltages other than 3 and 5 VDC?
It is fairly linear and you can change Rb proportionately with the voltage for the most part. There are different responses though: for better dynamic range 33 ohm and 56 ohm at 3v and 5v respectively, for better linearity 43 ohm and 75 ohm at 3v and 5v.

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…..)

Is there a pin for “cpol” (clock polarity)? It is referenced in the PNI 11096 ASIC data sheet but I can’t find it anywhere else. How is cpol set?
In the datasheet we are just stating the SPI communication standard we use, cpol=0 and this can not be changed for the ASIC.

I’ve implemented your discreet circuit design but it doesn’t seem to be working (or the sensor is oscillating at a much higher rate) what could be wrong?
The discreet circuit is a trick circuit and relies on less obvious specifications of the components, such as analog aspects of the digital gates and response curves of the analog components, therefore if any parts where substituted (even changing family) the circuit may not work properly

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 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.

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 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.

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 affect of changing Rb and will it damage the module if I don’t?
The Rb resistors are tuning resistors used to optimize the sensor performance for a particular applied voltage. Not changing Rb will not damage the module.

What is the bandwidth of the sensor?
The theoretical bandwidth is sample frequency / 2 though for our applications we are dealing with DC fields so therefore haven’t studied this much. The frequency is determined by the period select.

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

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

What is the purpose of the "VSTBY" pin? Does it have anything to do with a "standby" mode or does it just connect to a clamping diode?
VSTBY is power to the SPI port of the ASIC which should always be applied in order to prevent current sinking caused when another device is driving the SPI bus.

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.

What tests can be performed as an incoming inspection on the Sen-XY?
Basic opens shorts testing can be done. Values in the K ohm are open and values in ohms from pad to case are shorts. (I do not provide this information to module users; rather inform them to return for evaluation though some volume customers are aware of this issue).

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 are the Rb resistors that need to be changed for applied voltage on the board?
The Rb resistors are the sensor series resistors and have designators: R1,2,3,4,6,7.

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 can't I read the Z-axis sensor when a Micromag3 is plugged in?
The Z-axis sensor can oly be read in RAW mode as it can not be used as a 3-axis compass without tilt compensation therefore the Commboard purposely by design dows not calibrate or use the Z-axis in calculations.

Why do I have sensor zero offset?
This is caused by differences in the bias resistance which include the biasing resistors and the output impedance of the IC (ASIC).

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.

Why don’t I see a significant change in inductance?
a. Our spec sheet doesn't show change of inductance over the magnetic field, only the number of counts with varying magnetic fields since our recommended and supported drive circuitry doesn't require the customer to actually measure the exact inductance value. If the customer just measures the inductance without performing the front-back drive on our sensors, it will be temperature dependent. Although the properties of the sensor are changing inductance over changing magnetic fields, to get a robust temperature independent output from the sensors, we recommend it be connected to our ASIC. The count from the ASIC will provide the change in magnetic field. Details of the output count versus field strength can be found in the data sheet.

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.

Would the Micromag / ASIC work correctly if it receives a '16 bit' command, where the last 8 bits are zeros (or whatever)?
No it will not as the 8 bit command will be pushed out and the last 8 bits would be received as the command. The command register works like a shift register so the first 8 bits would shift clean through.

After sending a command byte can SSNOT be brought high while waiting for DRDY to go high and then taken low to read the sample data? From a big picture view, can I issue a command to the 11096 ASIC, and then use the SPI bus to talk to another device and finally come back to the 11096 ASIC to get the result of the previous command?
Yes, the SSNOT can be brought back high and the SPI bus used to talk to another device.

Can the ASIC be used with only one sensor?
Yes, the ASIC can be used with any combination from one to three sensors with any axis combination as well.

Is there a pin for “cpol” (clock polarity)? It is referenced in the PNI 11096 ASIC data sheet but I can’t find it anywhere else. How is cpol set?
In the datasheet we are just stating the SPI communication standard we use, cpol=0 and this can not be changed for the ASIC.

What is the purpose of the "VSTBY" pin? Does it have anything to do with a "standby" mode or does it just connect to a clamping diode?
VSTBY is power to the SPI port of the ASIC which should always be applied in order to prevent current sinking caused when another device is driving the SPI bus.

Would the Micromag / ASIC work correctly if it receives a '16 bit' command, where the last 8 bits are zeros (or whatever)?
No it will not as the 8 bit command will be pushed out and the last 8 bits would be received as the command. The command register works like a shift register so the first 8 bits would shift clean through.