FAQs

FAQs for the SmartSens family

FAQs for the MicroMag Modules

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 PNI's sensors be used to build detection devices?
Yes. PNI's magneto-inductive sensors have been used in a number of detection applications. One of the most common applications is the detection of a car passing by a specific area. Our sensors have been used in applications needing to detect objects as small as a bullet and as large as an ocean-going ship.

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 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 far away from your ASIC can your sensors be mounted?
Typical applications will have the ASIC placed within an inch of the sensors. However, it is possible to mount them remotely by running twisted pair wires to the sensors. We recommend two independent twisted pairs, as shown in this diagram:

Twisted Pair Sensor Diagram

How is PNI's magneto-inductive (MI) sensing different from a fluxgate or magneto-resistive sensing?
Magneto-inductive sensing has some particularly useful attributes that set it apart from other magnetic sensing technologies. Specifically: * The output is inherently digital. The output from PNI’s ASIC is a clearly defined number, and this number is directly related to the applied magnetic field. Most other technologies provide an analog output which require additional component hardware, such as amplifiers and analog-to-digital converters. * Very high resolution, on the order of 10 nT, can be obtained with the basic circuit. In comparison, competing technologies either cannot achieve this level of resolution due to inherent noise floors, or it can be comparatively expensive due to the need for costly external components. * Low power consumption. Power consumption with MI technology is inversely proportional to the sample rate, such that at an 8 Hz sample rate power consumption is typically 1.5 mW, while at a 300 Hz sample rate it is typically 7.5 mW. In comparison, magneto-resistive (MR) senors generally consume around 15 mW to 30 mW, making MI technology 2x to 20x more power efficient, depending on the implementation. * No need to set/reset MI sensors. Competitive technologies, such as MR, often require sending a high current pulse through the sensor in order to reset the magnetic domains within the core material. This pulse mandates the ability to generate a large peak power, on the order of several watts, and this power spike can cause problems with other components within a users system. Such a set/reset signal is not required with MI sensors. * Output is inherently stable over temperature. The reverse/forward biasing nature of PNI’s MI circuit athermalizes the output since changes in the bias resistance or inductance due to temperature are experienced in both the forward and revers directions, and are thus cancelled. * No hysteresis. PNI’s MI sensor design and the forward/reverse biasing nature of the MI circuit result in virtually no hysteresis. Since hysteresis directly affects the accuracy of measurement, PNI’s MI sensors can be used for applications that require high accuracy. See PNI's white paper entitled "Magneto-Inductive Technology Overview" for more information.

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 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, 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.

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 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.

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 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 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 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 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.

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.

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.

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.

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.

Does the MicroMag3 have pitch and roll outputs?
No, the MicroMag3 only provides raw magnetometer output.

Why doesn't my Micromag 3 give tilt compensated compass heading(s) 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.