i-Lotus M12M Manuale utente
01 May 2008 M12M™ Quick Start Guide (403-TTN-001) Page 1
M12M TM
Quick Start Guide
Prepared by:
i-Lotus Pte. Ltd.
Sales & Marketing Department
01 May 2008 M12M™ Quick Start Guide (403-TTN-001) Page 2
Contents
1Overview........................................................................................................................3
1.1 M12M Positioning Receiver ....................................................................................3
1.2 M12M Timing Receiver...........................................................................................3
2Product Highlights..........................................................................................................4
3Receiver Description......................................................................................................5
3.1 M12M Nominal Voltage and Current Ranges..........................................................6
3.2 Backup Battery (Externally applied backup power) .................................................6
4M12M Oncore Receiver Printed Circuit Board Mechanical Drawing...............................8
5Time RAIM Algorithm (M12M Timing Receiver Only).....................................................9
6Automatic Site Survey (M12M Timing Receiver Only)..................................................10
7100PPS Output (M12M Timing Receiver Only)............................................................11
8One Pulse Per Second (1PPS) Timing.........................................................................12
9I/O Commands.............................................................................................................17
01 May 2008 M12M™ Quick Start Guide (403-TTN-001) Page 3
1 Overview
This guide
1.1 M12M Positioning Receiver
The M12M Oncore is a 12-channel positioning receiver offering one of the fastest Time to
First Fix (TTFF) specifications in the industry, and split second reacquisition times.
1.2 M12M Timing Receiver
The M12M timing receiver is a variant of the M12M positioning receiver, and its highly
optimized firmware makes it one of the most capable timing receivers on the market.
Standard features include precise, programmable, one-pulse-per-second (1PPS) or 100
pulse-per-second (100PPS) outputs and features T-RAIM integrity monitoring algorithm.
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2 Product Highlights
Features present on all M12M receivers include the following:
12-channel parallel receiver design
Code plus carrier tracking (carrier-aided tracking)
Position filtering
Antenna current sense circuitry
Operation from +2.85 to +3.15 Vdc regulated power
3V CMOS/TTL serial interface to host equipment
3-dimensional positioning within 25 meters, SEP (with Selective Availability [SA]
disabled)
Latitude, longitude, height, velocity, heading, time, and satellite status information
transmitted at user determined rates (continuously or polled)
Straight 10-pin power/data header for low-profile flat mounting against host circuit
board. An optional right angle header is available for vertical PWA mounting.
Optional on-board Lithium battery
User selectable NMEA 0183 output
Additional features specific to the M12M positioning receiver include:
Support for inverse differential GPS operation
RTCM differential GPS support using second serial port
User controlled velocity filter
Additional features specific to the M12M timing receiver include:
Precise 1PPS output (+/- 25 ns accuracy) w/o sawtooth correction
Selectable 100PPS output
Automatic site survey
Time RAIM (Time-Receiver Autonomous Integrity Monitoring) algorithm for checking
timing solution integrity
01 May 2008 M12M™ Quick Start Guide (403-TTN-001) Page 5
3 Receiver Description
The M12M Oncore receiver provides position, velocity, time, and satellite tracking status
information via a serial port.
A simplified functional block diagram of the M12M receiver is shown below in Figure 3.1.
Figure 3.1: M12M Oncore Receiver Functional Block Diagram
A chart of the typical output voltage vs. the load current is shown below in figure 3.2. Note
that there is some drop to the output voltage as higher currents are drawn due to IR losses
across the current sense resistor and pass transistor. The system engineer should consider
this drop if the coax run to the antenna is going to be long, and/or the gain of the antenna
being used is adversely affected by lowered input voltage. Note that the can accept any
voltage from +2.5 to +5.5 Vdc on the antenna bias pin (Pin 9.)
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Figure 3.2 Antenna drive circuit performance
The following table lists the assigned signal connections of the M12M receiver's power/data
connector.
Pin #
Signal Name
Description
1
TxD1
Transmit Data (3V logic)
2
RxD1
Receive Commands (3V logic)
3
+3V PWR
Regulated 3Vdc Input
4
1PPS
1 pulse-per-second output
5
Ground
Signal and Power common
6
Battery
Optional External Backup
7
Reserved
Not currently used
8
RTCM In
RTCM correction input
9
Antenna Bias
3V-5V antenna bias input
10
Reserved
Not currently used
Table 3.1: Pin Designation
3.1 M12M Nominal Voltage and Current Ranges
Main Power
Voltage: 2.85V to 3.15V regulated, 50 mV peak-to-peak ripple
Current: 52 mA maximum (without antenna)
3.2 Backup Battery (Externally applied backup power)
Voltage: 2.2V to 3.2V
01 May 2008 M12M™ Quick Start Guide (403-TTN-001) Page 7
Current: 5 A typical @ 2.7V and 25C ambient temperature
Backup power retains the real-time-clock, position, satellite data, user commanded operating
modes, and message formatting.
01 May 2008 M12M™ Quick Start Guide (403-TTN-001) Page 8
4 M12M Oncore Receiver Printed Circuit Board Mechanical
Drawing
Figure 3.4: M12M Oncore Printed Circuit Board Layout with Straight, 0.050" [1.27mm] Pitch, 10
Pin Data Header
01 May 2008 M12M™ Quick Start Guide (403-TTN-001) Page 9
5 Time RAIM Algorithm (M12M Timing Receiver Only)
Time Receiver Autonomous Integrity Monitoring (T-RAIM) is an algorithm in Oncore timing
receivers (including the M12M T) that uses redundant satellite measurements to confirm the
integrity of the timing solution. The T-RAIM approach is borrowed from the aviation
community where integrity monitoring is safety critical.
In most surveying systems and instruments, there are more measurements taken than are
required to compute the solution. The excess measurements are redundant. A system can
use redundant measurements in an averaging scheme to compute a blended solution that is
more robust and accurate than using only the minimum number of measurements required.
Once a solution is computed, the measurements can be inspected for blunders. This is the
essence of T-RAIM.
In order to perform precise timing, the GPS receiver position is determined and then the
receiver is put into Position-Hold mode where the receiver no longer solves for position. With
the position known, time is the only remaining unknown. When in this mode, the GPS
receiver only requires one satellite to accurately determine time. If multiple satellites are
tracked, then the time solution is based on an average of the satellite measurements. When
the average solution is computed, it is compared to each individual satellite measurement to
screen for blunders. A residual is computed for each satellite by differencing the solution
average and the measurement. If there is a bad measurement in the set, then the average
will be skewed and one of the measurements will have a large residual. If the magnitude of
the residuals exceeds the expected limit, then an alarm condition exists and the individual
residuals are checked. The magnitude of each residual is compared with the size of the
expected measurement error. If the residual does not fall within a defined confidence level of
the measurement accuracy, then it is flagged as a blunder. Once a blunder is identified, then
it is removed from the solution and the solution is recomputed and checked again for
integrity.
A simple analogy can be used to demonstrate the concept of blunder detection and removal:
a table is measured eight times using a tape measure. The measurements are recorded in a
notebook, but one of the measurements is recorded incorrectly. The tape measure has 2
mm divisions, so the one-sigma (1) reading error is about 1 mm. This implies that 95% of
the measurements should be within 2 mm of truth. The measurements and residuals are
recorded in the table on the following page. From the residual list, it is clear that trial six was
a blunder. With the blunder removed, the average and residuals are recomputed. This time,
the residuals fall within the expected measurement accuracy. This is shown in Table 3.4
below.
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Trial
Measurement (m)
Residual (mm)
Status
New Residual (mm)
1
9.998
14.5
OK
2
2
10.001
11.5
OK
-1
3
9.999
13.5
OK
1
4
10.000
12.5
OK
0
5
10.002
10.5
OK
-2
6
10.100
-87.5
removed
7
9.999
13.5
OK
1
8
10.001
11.5
OK
-2
Ave
10.0125
10.000
Table 3.4: Blunder Detection Example
6 Automatic Site Survey (M12M Timing Receiver Only)
The Automatic Site Survey mode simplifies system installation for static timing applications.
This automatic position determination algorithm is user initiated and can be deactivated at
any time.
The Automatic Site Survey averages a total of 10,000 (slightly over 2 1/2 hours) valid 2D and
3D position fixes. If the averaging process is interrupted, the averaging resumes where it left
off when tracking resumes. During averaging, bit 4 of the receiver status words in the
Position/Status/Data Messages (@@Ha and @@Hb) is set. Once the position is surveyed,
the M12M timing receiver automatically enters the Position-Hold Mode. At this point, the auto
survey flag is cleared and the normal position-hold flag is set in the receiver status byte of
the @@Ha and @@Hb messages.
Once the antenna site has been surveyed in this manner, the user can expect a 2D position
error of less than 10 meters with 95% confidence, and a 3D error of less than 20 meters with
95% confidence.
Throughout the survey time the T-RAIM algorithm (if enabled) is active and is capable of
detecting satellite anomalies, however isolation and removal of the bad measurement is not
possible. Once the survey is completed, the T-RAIM algorithm is capable of error detection,
isolation, and removal.
Indice
