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Geophysical Sensor Recording
Recording data from Geophysical Instruments is the first step to creating Contour Zone maps, Elevation maps, Herbicide / Pesticide Application Maps,  Conductivity / Salinity, or Soil ph Maps.   HGIS PRO (with SensorTrack) can record RS232 and other types of data  from many devices.

A partial list of supported instruments:
Conductivity (GEONICS, DUALEM), Laser Rangefinders, Minota SPAD 502
Chlorophyl Meter , Honeywell HMR3000 Compass, Bar Code Scanners, Spectrum Penetrometers, RAE Volatile Organic Compound Monitors,  and User Defined Sensors.  Most Sensors that output "human readable" data records are supported. When designing  new sensors, we recommend NMEA style records up to 12 data fields per record as these are the most versatile and already supported by SensorTrack. New binary or non-standard sensors can be added with a custom programming charge.

One Sensor    Allegro

Recording Single Serial Sensors
Above left is a low cost system for recording a single sensor and GPS (yes, that is the GPS with the two blue lights).  This system is especially good for students, but is not waterproof.  This system includes a readily available Bluetooth GPS (Haicom SirfSTAR III WAAS GPS which yields 3 meter accuracy with full view of sky), Socket Cordless Serial Adaptor(CSA) from http://www.socketcom.com, and Windows Mobile 5 Computer with Bluetooth.  The RS232 sensor plugs into the CSA (above left).  The GPS and computer have batteries capable of 6-8 hours use, and can talk to the CSA and each other with no cables to either the GPS or Computer.  The trick is to set one Bluetooth device as incoming, and one as outgoing so the computer can talk to both units at the same time. Note: the CSA requires the RTS/CTS pin to be high. The CSA should work with most Sensors and SensorTrack, although an adaptor may be required to set the RTS/CTS pin high for many sensors as this is not standard (due to Bluetooth intereference, a little data loss sometimes occurs, but is not significant in most applications).

Above right is the Juniper Systems Allegro, a ruggedized waterproof handheld computer with two built-in serial ports.  It is recommended for harsh environments, although it is relatively expensive ( http://www.junipersys.com ).  The Allegro contains two ruggedized serial port connectors, one for the GPS and the other for the Sensor.

Alternate Serial

Other Serial Port Options
Plug-in Serial Cards as shown above will work with HGIS and SensorTrack. These are recommended only as temporary solutions as they may fail after awhile. The connectors are somewhat fragile. One and two port plug-in cards have been tested and work OK. None of the four port cards we have tested are recommended.

Internal serial ports (COM1) on handheld computers are often designed for ActiveSync (such as above lower left cable). These may not work with all devices. A GENDER CHANGER and NULL MODEM
(shown center above) are usually required with COM1. The TDS Recon, and Juniper Systems Allegro have normal COM1 Serial Ports, they do not require GENDER CHANGER or NULL MODEM, and they DO support all devices.

The Trimble AgGPS 132 can pass thru data from a Sensor connected to its Port B (NMEA mode only).  HGIS supports this for many sensors, but it takes some practice for a user to
correctly configure the GPS for this mode. This is not recommended with GEONICS or any sensor which requires software polling.

We recommend Windows Mobile 5 or later for Handhelds, especially if using Bluetooth.  If not using Bluetooth, Windows CE 4.2 is acceptable.  For Laptops, we recommend Windows XP or 2000.

Allegro 232BSS4            Three Sensor     

Logging Multiple Sensors with the 232BSS4
There are several ways to use the B&B 232BSS4 4-Port Serial Multiplexer with HGIS (232BSS4 is available from http://www.bb-elec.com ). The 232BSS4 is directly supported by HGIS, so no drivers are needed. The Serial NMEA GPS plugs into Port A and up to 3 Sensors may be plugged into ports B, C, and D.

Above left is the typical connection of the 232BSS4 with a ruggedized computer.  The Juniper Systems Allegro and TDS Recon are recommended for this configuration.  This system will work with any NMEA GPS receiver.

Above right uses a wireless connection to a Windows Mobile 5 Handheld comptuer.  The system shown includes a Trimble AgGPS 132 submeter GPS receiver, 232BSS4 Serial Multiplexer, Socket Bluetooth Cordless Serial Adaptor (CSA) from http://www.socketcom.com , and Windows Mobile 5 Computer with Bluetooth.    Any serial NMEA GPS may be used, so this system may either be low cost or high accuracy.  (Power to devices is not shown).

Below is the 232BSS4 connected to a Laptop Computer through its internal Serial Port.  Plug-in Serial cards are not as electrically reliable as computers with a Serial Port built-in. If you use plug-in serial cards, you should carry a spare card.

The small connectors in the bottom of iPaqs and similar computers may be used temporarily but are not as reliable as they may develop electrical problems after some time in the field. Having spare cables (when using low cost handhelds, carry spare computers) is recommended as you will need to troubleshoot problems in the field.

Laptop 232BSS4    EdgePort

Recording up to 15 Serial Ports with a Pentium Laptop
(2 port Serial - USB Adaptor shown)
Above right is a reliable system for logging up to 15 - RS232 ports using a fast Pentium Laptop.  Any Serial GPS (NMEA or TSIP) may be used depending upon accuracy required.  This solution uses the EdgePort Serial - USB Adaptors which are available with 2, 4, 8 and 16 port (2 port device shown above right). Multiple adaptors may be connected to the computer, but SensorTrack is limited to 15 ports plus the GPS. This system can record a total of 100 records per second from the sensors. We recommend shock mounting your Laptop in a foam filled aluminum case to minimize vibration and give the longest life.

We don't recommend Edgeport Serial - USB adaptors with Handheld Computers, as we haven't found a Handheld Computer that properly supports the Edgeport Serial - USB Adaptor. (Note: We have not tested the Juniper Systems Archer yet.)

Measuring Voltage
Some sensors output a voltage. Up to four voltage sensors may be connected to one Crossbow CXLDK A-D ( http://www.xbow.com/Products/productsdetails.aspx?sid=37 ) convertor which then connects to one serial port on the computer.  For example, to log 28 analog inputs, you would use 7 CXLDK converters connected to 8 serial ports (including 1 port for the GPS) of an EdgePort 8 Serial port to USB adaptor and a Laptop requiring only one USB port.

The input voltage range of the CXLDK is 0 - 4 volts at 12 bits; and can be modified by simple resistor networks for other ranges (for example: 0-12 volt, +/-5 volt, etc.)

SensorTrack can log each CXLDK at up to 25 times per second (25 Hertz).  Some users are able to log faster than 25 Hertz (80-120 Hertz), depending upon CPU speed, number of CXLDK convertors, and other hardware. Test your complete system if you want to log faster than 25 Hertz as this is not guaranteed; however, the speed you get during testing should be the same as you will get in the field.

Measuring Shaft Rotation,
Frequency Counter, Event Counter,
and On/Off Inputs
SensorTrack provides the capability to measure low frequencies with very high accuracy.  For example, you want to know the speed of a shaft every second. The shaft is rotating between 100 RPM and 30000 RPM with a magnet mounted on the shaft and a magnetic switch mounted nearby.  This function can measure shaft rotation to 4 significant digits each second.  For example you might read 13.93 Hertz or revolutions per second (which is equal to 835.8 RPM).  This can give you 100 times the resolution of other counter solutions for low speed shafts. These inputs can also measure frequency, count events, or monitor the presence of a voltage from a switch or other sensor.

SensorTrack monitors up to 3 input pins on any open SensorTrack Serial Port (not the GPS Port, 232BSS4 ports, USB ports, or Bluetooth ports).   Laptops with built-in Serial Ports are best for this kind of measurement, many handhelds with built-in ports may work (sometimes not all inputs are implemented).  Each of the three inputs may measure Frequency, Events, or On/Off.  A frequency might come from a load cell with frequency output, or magnetic shaft sensor.  Events could come from a Geiger Counter, a corn stalk sensor; or other device not producing a frequency.  On/Off could be the position of a switch, or whether voltage is being applied to a relay, etc.  "Sample Period" may be from 1 to 60 seconds.

You can measure frequencies from 2 - 500 hertz (100 RPM to 30000 RPM). The maximimum is 500 transitions per second (hertz) total for all pins monitored.  For highest accuracy, do not run other applications (besides HGIS) while sampling counter inputs.  A one second measurement interval provides about four significant digits (for example: 60.03 hertz).  A four to six second interval provides about five significant digits (e.g.60.026 hertz).  The computer’s internal clock is used for timing which may vary slightly from one computer to another (typically +/-0.05%).  This accuracy is acceptable for most applications.

You will need to make a custom cable to bring out these wires from the serial port.  Each input will read "OFF" if the voltage is between 0.0 and +0.4 volts; or a "ON" if the voltage is between +3 and +12 volts. Do not connect the input directly to motors, pumps, solenoids, or other inductive loads without protective circuitry.  If used without proper protection, inductive voltage spikes may damage the electronics. It is recommended that you always use a 2.2Kohm to 4.7Kohm protective resister in between the sensor and the input to protect against short circuits and voltage spikes.  Test your hardware to determine its capability.

Sensor Data Logging

Each input port can log data to a TXT file and/or to a Map Layer.  When logging to a TXT file, the maximum rate depends upon the hardware. Slower computers can log at least 20 records per second to a TXT file. With fast Pentium computers 100 records per second or more may be logged.   TXT files can contain many millions of Records.  TXT files are best when logging data faster than 1 record per second.  When drawing Sensor data to a map layer, the maximum data rate is 1 point per second per port. The maximum number of points that can be logged to a map layer is usually in the thousands or tens of thousands.  Map Layers are used when logging data at slower than 1 record per second. For example, if you are logging sensor data every 3 seconds for a few hours, you could use either a TXT file or a Map Layer. 

Configuration can get complicated with a lot of sensors; however, you don't need to setup SensorTrack every time.  Just set everything up once, make sure it is all working, then save a Settings file.  Then select the settings file at startup to open all the ports and configure everything. 
SensorTrack allows each port to be configured separately, so even if you have 15 ports, they can all be independent.  Data can be collected at a different rate for each port, some ports could be every sensor record; other ports could be based on time or distance.

GPS Considerations

First, decide what accuracy you need and want to pay for.  We test all GPS receivers at 95% confidence (the same as surveyers do).  This means that 95% of the time, the GPS will be within this specification. See our page on this website on submeter GPS for more details on how we test.  Be very skeptical of GPS Manufacturers claims. A few GPS Manufacturers are conservative; however, many publish somewhat misleading claims.

There is a simple way to tell how good your GPS is with a clear view of the sky.  If it has maps and navigation built-in, then it is about 3-10 meters independent of the cost (even  the expensive ones).  For other types of GPS, use the following guidline.  If the GPS retails for less than US$250, then it can be within 3-5 meters.  If it retails for US$450-US$1500, then it should be around 2 meters.  If it retails for US$2000-US$4000, then it is probably about 1 meter. If it retails for above US$5000, then it should be better than 1 meter. This is with a clear view of the sky, any GPS will be worse if part of the sky is blocked by your body or other objects.  There are other factors affecting GPS accuracy, so any GPS will be off sometimes, that is why they are specified for 95% of the time.

Plug-in GPS receivers (such as Navman Sleeve, Compact Flash, and SD Card) are only recommended with an external antenna. Your body blocks too many satellites for the GPS to work very well with the internal antenna. The GPS only has a clear view of the sky when it can see close to the horizon all the way around.


the leader in
Handheld Geographic Information Systemstm

GPS Mapping
Soil Sampling
Instrument Recording
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Contact Us
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Last Updated:  January 24, 2006