SD Card Data Capacity

A typical string of data for each sample logged by the SpaceLogger A10 would be as follows:
Prefix, Date, Time, Channel 1, Units for Channel 1, Channel 2, Units for Channel 2, Switch State<CR><LF>

Where:

Prefix:	text set by user - may be up to 10 characters long
Date:	format is DD/MM/YYYY (10 characters)
Time:	format is hh:mm:ss (8 characters)
Channel 1:	recorded value could be up to 16 characters max, including decimal point
Units 1:	text set by user - may be up to 10 characters long
Channel 2:	recorded value could be up to 16 characters max, including decimal point
Units 2:	text set by user - may be up to 10 characters long
Switch Sate:	logged as 0 or 1 (1 character)
<CR><LF>:	end of line is 2 characters

Therefore, max number of characters in one sample is 90, i.e. 90 bytes (including the comma delimiters).

If logging a sample once per second, for one month this would be approximately 250 MB of data in total.

The following table gives the approximate capacity of the SD card, depending on the logging interval selected and the actual size of the data sample recorded:

	SpaceLogger A10 Data capacity by sample size and logging rate
Memory Card Size	90bytes @ 1 per sec	90bytes @ 1 per 5 sec	45bytes @ 1 per sec	45bytes @ 1 per 5 sec
2 GB	8 months	>3 years	16 months	>6 years

Examples of SpaceLogger A10 Applications

Example of SpaceLogger A10 application

Logging of data from 2 analogue 4-20mA channels

Recording the level of water in a tank using an ultrasonic ranger

In this example we will use the low cost Devantech SRF06 ultrasonic ranger with 4-20mA output. It has an output current specified as 4mA + 31.37uA/cm

For channel 1 the value output by the logger is given by

C1 = (A1 + OFFSET1) x SCALE1 x 10^POWER1

Where

A1 is the measured value in mA x 100
OFFSET1 is the offset in mA x 100
SCALE1 is the scaling factor
POWER1 is the exponent for the power of 10 multiplier

So if we wish to record d the distance from the sensor to the water surface in metres OFFSET1 = - 4 x 100 = - 400

The scale value we require is the number of meters per 1/100th of a mA

SCALE1 x 10^POWER1 = 0.01/3.137  meters per 1/100th of a mA

= 0.0031878  meters per 1/100th of a mA

The logger uses integer maths and requires a value in the range +/- 32767 for SCALE1 so we can use 31878 with a multiplier of  10-7 to position the decimal point correctly.

SCALE1 x 10POWER1 = 31878 x 10-7

As 1/100th of a mA represents just over 3mm it is adequate to record 2 decimal places so

DP1 = 2

The following commands could therefore be used to setup the logger

SCALE1= 31878
OFFSET1= -400
POWER1= -7
DP1= 2
RATE= 10
MODE= NORMAL
FORMAT= P T C1 U1
TRIGGER= SO
PREFIX="Tank1"
UNITS1="m"

The recorded data would look similar to:

Tank1,15/03/12,12:44:40,0.22,m
Tank1,15/03/12,12:44:50,0.22,m
Tank1,15/03/12,12:45:00,0.22,m
Tank1,15/03/12,12:45:10,0.22,m

Recording GPS data and two analogue channels

If it is required to synchronise readings from a number of loggers in different locations, eliminate any issues with real time clock drift or just know the location of the reading then the ability to connect a GPS to the logger is really useful.

In this example every 10 seconds we will record the RMC sentence from a GPS receiver which provides date, time, position, speed and course over ground information and readings from two 4 – 20mA sensors.

There are a number of GPS receivers that have RS232 outputs that are suitable for connecting to the logger, Garmin produce the GPS 35 HVS or GPS35 PC for example.

The logger needs to operate in slave mode and set to capture the RMC sentence every 10 seconds which is done by specifying a start string that requires the least significant digit of the time (UTC) field must to be 0

STX="$??RMC,?????0"

Question marks represent characters that can have any value.

The carriage return character can be used to identify the end of the RMC sentence and will be replaced by the analogue readings when data is recorded.

The following commands could be used to setup the logger

SCALE1=1
OFFSET1=0
POWER1= -2
DP1=2
UNITS1="mA"
SCALE2=1
OFFSET2=0
POWER2= -2
DP1=2
UNITS2="mA"
FORMAT= P C1 U1 C2 2
PREFIX="A10"
MODE= SLAVE
STX="$??RMC,?????0"
ETX=13     // decimal value of ASCII carriage return character
BAUD=4800  //NMEA tandard baud rate
OUTPUT= C

Example of the recorded data:

$GPRMC,110150.739,A,5045.2096,N,00131.6903,W,0.00,,020412,,*05,A10,8.89,mA,9.90,mA
$GPRMC,110200.739,A,5045.2087,N,00131.6868,W,0.00,,020412,,*0F,A10,8.89,mA,9.90,mA
$GPRMC,110210.738,A,5045.2084,N,00131.6883,W,0.00,,020412,,*09,A10,8.89,mA,10.20,mA
$GPRMC,110220.738,A,5045.2085,N,00131.6892,W,0.00,,020412,,*0B,A10,8.89,mA,10.20,mA
$GPRMC,110230.737,A,5045.2088,N,00131.6886,W,0.00,,020412,,*0D,A10,8.89,mA,10.20,mA
$GPRMC,110240.736,A,5045.2102,N,00131.6912,W,0.00,,020412,,*04,A10,8.89,mA,10.20,mA

Analogue to RS232 converter

The logger can operate without a memory card just to provide an analogue to RS232 converter function.

To do this the output should be set to continuous.

For example the following commands in the SETUP.TXT file would give the output shown above

SCALE1=1
OFFSET1=0
POWER1= -2
DP1=2
RATE=1
MODE= NORMAL
FORMAT= P T C1 U1
OUTPUT= C
PREFIX="#A10"
UNITS1="mA"

Push button triggered reading

The SpaceLogger can be setup to record a single reading each time a switch is closed.

The switch could be a simple push button or for example some kind of position/object detection switch.

If required there can also be a programmable delay after the switch is closed to allow the sensor to stabilise before recording the reading.

The SpaceLogger MODE must be SINGLEso repeated readings are not recorded if the button is held closed.

The RATE setting has no effect when in single mode. The logger takes a reading every second but only records the single required reading. It will not record readings at more than once a second.

As an example the following commands in the SETUP.TXT file would record a reading 5 seconds after the push button is pressed.

SCALE1=1
OFFSET1=0
POWER1= -2
DP1=2
RATE=1
MODE= SINGLE
FORMAT= P T C1 U1
TRIGGER= SC
DELAY=5
PREFIX="#A10"
UNITS1="mA"

If an indication that a reading has been taken is required a high efficiency led (Avago HLMP-K155 RS 826-521 Farnell 100-3210) can be connected to the alarm output and the alarm condition set to logging by including the following command in the SETUP.TXT file.

ALARM=L

The LED will come on shortly after the switch is pressed and remain on during the delay until the reading is recorded.

Logging the supply voltage

Often it is useful to record the supply voltage this can be done with a simple resistor between the supply and one of the analogue inputs.

The choice of resistor value will depend on the accuracy required, acceptable current draw and supply voltage range.

The current through the resistors is
I = V/( R + 47 + 130 )

To record the reading in volts we require the volts per 0.01 mA
SCALE1 x 10^POWER1 = 0.00001 x ( R + 177 )

For R = 4700 ohms this would give
SCALE1 x 10^POWER1 = 0.04877

So we can use
SCALE1 = 4877
POWER1 = -5

The maximum voltage V is limited by the maximum allowable voltage across the 130 ohm resistor of 3 volts. Note V must always be positive.

The following commands could be used to setup the logger

SCALE1= 4877
OFFSET1= 0
POWER1= -5
DP1= 1
RATE= 10
MODE= NORMAL
FORMAT= P T C1 U1
TRIGGER= SO
PREFIX="V1"
UNITS1="volts"

The recorded data would look similar to

V1,15/03/12,12:44:40,13.4,volts
V1,15/03/12,12:44:50,13.4,volts
V1,15/03/12,12:45:00,13.5,volts
V1,15/03/12,12:45:10,13.5,volts

Extending the number of analogue channels

If two 4 to 20mA channels is not enough, the number of channels can be extended by daisy chaining SpaceLogger A10s together.

The first logger in the chain determines the frequency and/or conditions for measurements, the rest of the units operate in slave mode appending their data to the received data. The last unit in the chain stores the data on to the SD card.

Set up commands for the first logger:

SCALE1=1
OFFSET1=0
POWER1= -2
DP1=2
UNITS1="mA"
SCALE2=1
OFFSET2=0
POWER2= -2
DP2=2
UNITS2="mA"
RATE=10
MODE= NORMAL
FORMAT= P T C1 U1 C2 U2
OUTPUT= C
TRIGGER= SO
PREFIX="Ch1-8"  //will be used to identify the start of the reading by subsequent loggers

Set up commands for loggers 2 to 4:

SCALE1=1
OFFSET1=0
POWER1= -2
DP1=2
UNITS1="mA"
SCALE2=1
OFFSET2=0
POWER2= -2
DP2=2
UNITS2="mA"
MODE= SLAVE
FORMAT= C1 U1 C2 U2
OUTPUT= C
STX="Ch1-8" // start of string output by logger 1
ETX=13      // decimal value of ASCII carriage return character

Data recorded

Ch1-8,15/03/12,12:44:40,8.89,mA,9.90,mA,5.85,mA,9.10,mA,15.19,mA,7.90,mA,8.82,mA,13.64,mA
Ch1-8,15/03/12,12:44:50,8.89,mA,9.90,mA,5.85,mA,9.10,mA,15.19,mA,7.90,mA,8.82,mA,13.64,mA
Ch1-8,15/03/12,12:45:00,8.89,mA,9.90,mA,5.85,mA,9.10,mA,15.19,mA,7.90,mA,8.82,mA,13.64,mA
Ch1-8,15/03/12,12:45:10,8.89,mA,9.90,mA,5.85,mA,9.10,mA,15.19,mA,7.90,mA,8.82,mA,13.64,mA

Physical	Enclosure dimensions	Width: 67 mm Depth: 67 mm Height: 28 mm (excluding optional rubber feet)
	Weight	75g
	Enclosure material	GP ABS (UL94-HB) plastic and acrylic
Connections	Type	Screwless terminals capable of accepting wire 0.32 to 0.65mm diameter (AWG 28 to 22)
Analogue Input	Number of Channels	2
	Range	4 to 20 mA (0 to 23 mA maximum)
	Sampling	Readings are sampled at 75 Hz and averaged over 1 sec
	Maximum logging rate	1 Hz
	Input impedance	177 ohms
	Accuracy	±1% or 0.1 mA at 20 °C over range 4 to 20 mA
	Drift with temperature	100 ppm / °C over range -40 °C to +40 °C
	Analogue to digital converter	10-bit resolution
Switch Input	Digital channel	Input for logging control switch
	Max input voltage	Must not exceed 3V
	Current out	7μA max
RS232 Input	Number of channels	1
	Transmission standard	RS232 compatible, 8 bits and no parity
	Transmission speed	9600 Baud (default) or selectable from 115200, 57600, 38400, 19200, 4800, 2400, 1200, 300 or 110 Baud
	Data sample	Records only the data between specified start (STX) and end (ETX) characters
RS232 Output	Transmission standard	RS232 compatible, 8 bits and no parity
	Transmission speed	9600 Baud (default) or selectable from 115200, 57600, 38400, 19200, 4800, 2400, 1200, 300 or 110 Baud
	Output rate	Normal Mode: 1 data record per 1 to 60 seconds - selectable Single sample Mode: single data record output in response to event defined by command TRIGGER Slave Mode: rate determined by input of RS232 data sample defined by STX and ETX
Alarm Output	Min output voltage	VOH=1.7V Typ @ 1mA output current
Data Storage	Data storage card	Removable SD, MMC or MMC mobile card
	Data capacity	2 GByte (max)
	File system	FAT16 or FAT32 with 8.3 file names Sector size 512 Bytes
	Data logging interval	Normal Mode: 1 data record per 1 to 60 seconds - selectable Single sample Mode: single data record logged in response to event defined by command TRIGGER with time delay defined by command DELAY Slave Mode: rate determined by input of RS232 data sample defined by STX and ETX
Audible / Visual Indicators	LED indicators	Green: Ready to record data Red: Power on, Writing data to SD card
	Audio bleeper	Two tone signal on correct card insertion Single tone when data purge button depressed Four bleeps per minute when time and date not set
Real Time Clock	Accuracy	±40 ppm at 25°C
	Backup battery	CR2032
Power	Power requirement	7 to 30 V DC
	Current at 12 VDC	10 mA typical
	Supply input protection	Polarity reversal protected and internal resettable 140 mA fuse
	Connection options (both included)	1.3 mm centre pin DC connector, or Screwless terminals (0.32 to 0.64 mm diameter, AWG 28 to 22 conductors)
Environmental	Temperature range	Operating: -25°C to +70°C [or dependent on card conditions] Storage: -40°C to +70°C
	Enclosure protection	IP203
	EMC	EMC Directive 89/336/EEC - CE marked (Emissions: EN61326:1997 inc A1/A2/A3:2003, EN60945:1997 Immunity: EN61326:1997) FCC/CFR 47: Part 15:2004

The manufacturer reserves the right to amend the specification and therefore the information in this document may be subject to change.