Texas instruments CBL 2 Technical Reference
CBL 2™
Technical Reference
Calculator-Based Laboratory, CBL, and CBL 2 are trademarks of Texas Instruments Incorporated.
LabPro is a trademark of Vernier Software & Technology.
Santoprene is a registered trademark of Monsanto.
2000 Texas Instruments Incorporated. All rights are reserved.
Contents
Introduction 5
Miscellaneous Reference Information 5
CBL 2 Software Upgrades 5
Data Collection Modes 5
Realtime Sampling 5
Non-Realtime Sampling 6
FastMode Sampling 6
Mode Comparison Table 7
Beep Sequences 8
Archiving in CBL 2’s
Memory 9
FLASH
Technical Specifications for Sensors 10
TI Light Sensor 10
TI Light Sensor Specifications 10
Stainless Steel Temperature Sensor 10
Stainless Steel Temperature Sensor Specifications 11
Temperature Accuracy 12
Stainless Steel Temperature Sensor Chemical Tolerance 12
TI Temperature Sensor Note 13
TI Voltage Sensor 13
Auto-ID Sensors 14
Custom Sensors 15
Connector Pinouts 16
Programming the CBL 2 17
Digital Output Buffer 17
Digital Output Buffer Example 17
Triggering and Thresholds 18
Measuring Period and Frequency 19
Example: Measuring Frequency 20
Asynchronous/ Synchronous Triggering versus Record Time 21
Example 21
CBL 2 Command Summary 22
Command 0 Reset CBL 2 RAM 23
Command 1 Channel Setup 23
Command 2 Data Type 26
Command 3 Trigger Setup 26
2 CBL 2 Technical Reference
Command 4 Conversion Equation Setup (Analog) 28
Command 4 Sonic Temperature Compensation (Sonic) 30
Command 5 Data Control 30
Command 6 System Setup 31
Command 7 Request System Status 31
Command 8 Request Channel Status 33
Command 9 Request Channel Data 33
Command 10 Advanced Data Reduction 33
Command 12 Digital Data Capture 34
Command Sequence 34
General Information 36
Additional Notes on Command 12 41
Command 102 Power Control Command 41
Command 115 Check Set-up Information 41
Command 116 Check Long Sensor Name 42
Command 117 Check Short Sensor Name 43
Command 1998 Set LED Command 43
Command 1999 Sound Command 43
Command 2001 Direct Output to Digital-Out Port 43
Command 201 Archive Operations Command 44
Programming Examples 49
Example 1: Temperature Non-Realtime Data Collection 49
Example 2: Temperature Realtime Data Collection 49
Example 3: Distance and Velocity Non-Realtime
Data Collection 49
Example 4: Multiple Channels Non-Realtime Data Collection 50
Example 5: Conversion Equation Setup (Command 4) 50
Example 6: Data Control Setup (Command 5) 51
Example 7: Digital In Data Collection 51
Example 8: Digital Out 51
Example 9: CBL 2 LED Display 52
Example 10: Playing Music on the CBL 2 52
Example 11: Command 8 Program 52
Example 12: Command 9 Program 53
Example 13: Command 10 Program 53
Example 14: Archive Program (Command 201) 54
CBL 2 Technical Reference 3
Appendix A: Glossary A-1
Appendix B: CBL 2 Error Messages B-1
Appendix C: DataMate Sensor Setup Default Settings C-1
4 CBL 2 Technical Reference
Introduction
This technical reference is intended for CBL 2 users who want to write their own
programs for CBL 2 and Texas Instruments graphing calculators. This document includes
technical data such as specifications for sensors, syntax for CBL 2 commands, sample
programs, error codes, and miscellaneous other topics.
Instructions for using CBL 2 with the DataMate program or app are given in
Started with CBL 2
not addressed in this technical reference except for
Setup Default Settings
used by the DataMate program.
, which is included in the CBL 2 package. The DataMate program is
Appendix C: DataMate Sensor
. This table shows the default sensor settings and calibrations
Miscellaneous Reference Information
CBL 2 Software Upgrades
The CBL 2 uses
without buying a new CBL 2. As new functionality becomes available, you can
download the software from the TI web site to your PC and then use the TI-GRAPH
LINKé (sold separately) to upgrade your CBL 2.
Check the TI website (
compatibility statements. Directions for downloading upgrades will be given on the
web site.
FLASH
technology, which allows you to easily upgrade to new software
www.ti.com/calc
) for upgrades, paying special attention to
Getting
Data Collection Modes
On the CBL 2, data can be collected in one of three modes: realtime, non-realtime or
FastMode.
♦
In
realtime
after each point is taken.
♦
In
non-realtime
all of the data points are taken and then sends it to the calculator.
♦
In
FastMode
very fast sample rate, stores it internally until all of the data points are taken, and
then sends it to the calculator.
It is the default to return the time with the data collected.
CBL 2 Technical Reference 5
data collection, the CBL 2 collects data and sends it to the calculator
data collection, the CBL 2 collects data and stores it internally until
data collection, the CBL 2 collects data on a single analog channel at a
Realtime Sampling
In realtime data collection, the CBL 2 sends each data point to the calculator as it is
taken, so some data can be lost if the calculator is not ready to accept the data. In
addition, the quantity of data that can be collected is limited by the size of the
calculator memory.
Realtime data collection is used for:
♦
Slower sampling where the user wants to see the data as it is being collected.
♦
Very long data collection times where the CBL 2 may run out of memory during
data collection.
♦
Situations where the host calculator must process the data as soon as it becomes
available (such as to control an output in response to a temperature input).
This data collection mode should not be used for data collection of more than a few
points each second because the host calculator will not be able to keep up. In addition,
because of the nature of realtime data collection, the period/frequency and Command
12 channels cannot be sampled in this mode.
Since the number of points to be collected may not be known at the start of sampling,
set the “number of samples” to M1 when sending Command 3. This tells the CBL 2 to
take data but not send it to the host calculator until the calculator requests data.
Non-Realtime Sampling
In non-realtime data collection, the samples are taken and stored in the CBL 2 memory
until all the data has been collected. Then the data is sent to the host calculator. The
quantity of data collected is not limited by the size of the calculator memory, but is
limited by the size of the CBL 2 memory. Up to 12,000 samples max (or less under some
conditions) can be collected in non-realtime.
Non-realtime data collection is used for fast sampling of multiple channels and when
triggering is required.
All of the channels can be used in this mode, and the Command 12 functions can be
used. The sample time is limited by the number and types of channels enabled. For a
E
single channel, the sampling can be as fast as 1
calculator communication is maintained during the sampling. This allows the host
calculator to issue a Command 7 or Command 8 to ascertain the progress of the
sampling without disturbing the sampling process.
-4 second. In addition, normal
FastMode Sampling
FastMode sampling is designed to be used where a single channel must be sampled at
very fast sample times. This mode is used primarily when sampling sound using the
microphone.
6 CBL 2 Technical Reference
In general, FastMode is identical to non-realtime sampling with the following
exceptions:
♦
The sampling is limited to a single analog channel when doing FastMode sampling.
♦
The selected channel must not be in operation mode 5, 6, or 7.
♦
The communications with the host calculator are turned off during FastMode
sampling.
Note: In FastMode sampling, it is very important that the program not issue a GET command
until after sampling has been completed. If the CBL 2 receives a GET command it will abort
FastMode sampling with an error in order to respond to the GET command.
In FastMode, the sample times can be as fast as 20 msec (a sample frequency of 50KHz).
Mode Comparison Table
The table below shows some of the differences between the data collection modes.
Order of data
returned when
doing the GETs
from the host
calculator
Number of samples
limited?
Sample time limits
(approximate)
Number of
channels limited?
Realtime Mode
{ch1_1, ch2_1, …
deltatime_1}
{ch1_2, ch2_2, …
deltatime_2}
:
:
{ch1_n, ch2_n, …
deltatime_n}
Not by CBL 2, but
may be limited by
the host calculator
Sample Time > .25
second to 16000
seconds
Yes, only CH1-3
and 11
Non-Realtime
Mode
{ch1_1, ch1_2, …
ch1_n}
{ch2_1, ch2_2, …
ch2_n}
{ch3_1, ch3_2, …
ch3_n}
{time_1, time_2, …
time_n}
Yes, limited by
available memory
in CBL2
Sample Time ‚ 1e-4
seconds to 16000
seconds
No Yes, only a single
FastMode
Same as NonRealtime
Same as NonRealtime
Sample Time ‚ 2e-5
seconds to 1e-4
seconds
channel from CH1
to CH3
Can use
Triggering?
Communication
maintained during
sampling?
CBL 2 Technical Reference 7
No Yes Yes
Yes Yes No
Beep Sequences
The CBL 2 makes four kinds of sounds:
♦
A low tone followed by a high tone (low-to-high beep).
♦
A medium tone followed by another medium tone (medium-medium beep).
♦
A high tone followed by another high tone (high-high beep).
♦
A “tick” sound when a key is pressed.
The following bullets explain when beep sequences normally occur and what the beep
sequences mean.
♦
When the CBL 2 completes initialization, you will hear the startup sequence: highhigh beep, medium-medium beep, low-to-high beep (6 total beeps, plus LEDs light
up in this order: red LED, yellow LED, and green LED)
♦
When you press the QUICK SETUP button:
the medium-medium beep sounds if a sensor is attached to the CBL 2.
−
the high-high beep sounds if no sensors are attached to the CBL 2.
−
♦
When the CBL 2 is connected to a calculator during sampling commands:
the medium-medium beep sounds when initializing data collection.
−
the medium-medium beep sounds when starting data collection (transition from
−
pre-store to store).
the medium-medium beep sounds when completing data collection.
−
Note: If the sampling timing causes the beeps to run together, the CBL 2 software may not
sound all the beeps.
Note 2: You will not get all the beeps when Fast Sampling is enabled.
Note 3: You will not get all the beeps when using triggering.
♦
When you set the CBL 2 for manual trigger and press the START button, a mediummedium beep sounds.
♦
When you press the TRANSFER BUTTON:
the low-to-high beep sounds when the transfer succeeds.
−
the high-high beep sounds if the transfer fails for any reason.
−
♦
When an overcurrent condition is detected, five high-high beeps sound. (This causes
an error, which causes even more beeps to sound.)
♦
When the CBL 2 begins a full self-test, three low-to-high beeps sound.
♦
When self-test completes:
the low-to-high beep sounds if self-test passes.
−
the high-high beep sounds if self-test fails.
−
8 CBL 2 Technical Reference
When the CBL 2’s base code detects an error in the commands sent from the host, a
♦
high-high beep sounds twice.
When the CBL 2 powers up:
♦
two high-high beeps sound if the base code is not loaded.
−
three high-high beeps sound if the power-up self-test fails.
−
During base code download, three high-high beeps sound when any errors occur.
♦
(The unit resets and then the two high-high beeps mentioned in the previous bullet
sound.)
Archiving in CBL 2’s
The
FLASH
allowing updates to the operating system and storing the DataMate programs, the
FLASH
To preserve collected data so that it can be retrieved at a later time, data sets can be
stored in the
data set can be given a name.
You can write a program on the calculator to review the list of stored data sets and
♦
retrieve the desired one for further analysis. (See the sample archive program on
page 56.)
You can use the DATADIR program (available on the TI Resource CD or on the TI
♦
web site at
DATADIR program are given in
The
FLASH
convenient location for storing frequently used programs or as a temporary storage to
create more available memory on the calculator.
Command 201, in conjunction with the Link menu on the calculator, provides access to
these
memory in the CBL 2 can be used for several purposes. In addition to
memory serves as an archive space for other programs and data.
FLASH
archive can also store calculator programs and applications. This provides a
FLASH
archive operations. For details about Command 201, see page 44.
archive. To distinguish between different stored data sets, each
www.ti.com/calc
FLASH
) to manage
Memory
FLASH
Getting Started with CBL 2
memory. Directions for using the
.
CBL 2 Technical Reference 9
Technical Specifications for Sensors
TI Light Sensor
The TI light sensor uses a phototransistor to measure relative irradiance. The units of
irradiance are milliwatts per square centimeter. The light sensor’s output is a voltage
that is linearly proportional to the amount of irradiance it senses. The range of light
2
over which the sensor is sensitive is 10µW/cm
to 1mW/cm2.
The
auto-ID
measured voltage to relative units. The sensor is direction dependent and achieves the
highest output when the end of the sensor is pointed directly at the light source.
The light sensor is sensitive in the visible and near-infrared (
you can use it with
is designed to work in air only—it is not waterproof.
The light sensor returns
vary from light sensor to light sensor. The light sensor readings are also sensitive to
temperature.
resistor in the sensor causes the CBL 2 software to automatically convert the
) light range. This means
IR
emitting diodes as well as all visible light sources. The light sensor
IR
relative
readings, not absolute irradiance readings. Values may
TI Light Sensor Specifications
Channels Connects to
channels)
Current drain 5 mA max.
Voltage range 0–5 Volts
Irradiance range 10µW/cm2 to 1mW/cm2 (approximately)
Spectral response range 300nm to 1100nm (nanometers) (non-flat
response)
CH1, CH2, CH3
(analog
Chemical tolerance None (air only)
Pins used 2 ground
4 auto-ID resistor
5 +5 Volts DC
6 Signal
Stainless Steel Temperature Sensor
The Stainless Steel Temperature Sensor is an auto-ID general-purpose laboratory
temperature sensor that comes with your CBL 2. The sensor is rugged and durable, and
is designed to be used as you would use a thermometer for experiments in chemistry,
physics, biology, earth science, and environmental science.
10 CBL 2 Technical Reference
This probe uses the 20 kΩ NTC Thermistor. The thermistor is a variable resistor whose
resistance decreases nonlinearly with increasing temperature. The best-fit
approximation to this nonlinear characteristic is the Steinhart-Hart equation. The CBL 2
or CBL interface measures the resistance value, R, at a particular temperature, and
converts the resistance using the Steinhart-Hart equation:
T = [K
where T is temperature (°C), R is the measured resistance in kΩ, K
-
= 2.22468 X 10
K
1
4
, and K2 = 1.33342 X 10-7. Fortunately, CBL 2 and CBL take care of this
+ K1(ln 1000R) + K2(ln 1000R)3]-1 – 273.15
0
= 1.02119 X 10
0
conversion for you, and provide readings in °C (or other units, if you load a different
calibration).
Stainless Steel Temperature Sensor Specifications
Channels Connects to CH1, CH2, CH3 (analog channels)
Current drain 0.5 mA max.
Temperature range -25 to 125°C (-13 to 257°F)
Maximum temperature
sensor can tolerate
without damage
10-bit resolution 0.32°C (-25 to 0°C)
Temperature sensor 20 kΩ NTC Thermistor
150°C
0.12°C (0 to 40°C)
0.4°C (40 to 100°C)
1.0°C (100 to 125°C)
-
3
,
Accuracy ±0.2°C at 0°C, ±0.5°C at 100°C
Response time 95% of full reading: 11 seconds
98% of full reading: 18 seconds
100% of full reading: 30 seconds
Probe dimensions Probe length (handle plus body): 16 cm
Stainless steel body: length 11 cm,
diameter 4.0 mm
Probe handle: length 5.0 cm, diameter 1.25 cm
Pins used 2 Ground
3 Vres
4 auto-ID resistor
6 Signal
CBL 2 Technical Reference 11
Temperature Accuracy
This probe provides very accurate temperature readings. Near 0°C, readings are
accurate to ±0.2°C; near 100°C, readings are accurate to 0.5°C.
Important:
you cannot re-calibrate this sensor. Probe-specific calibrations should not be necessary
when using this sensor.
Because of the non-linear nature of the Stainless Steel Temperature Probe,
Stainless Steel Temperature Sensor Chemical Tolerance
The body of this sensor is constructed from grade 316 stainless steel (0.08% carbon,
2.0% manganese, 0.75% silicon, 0.04% phosphorus, 0.03% sulfur, 16-18% chromium,
10-14% nickel, 2-3% molybdenum, and 0.1% nitrogen). This high-grade stainless steel
provides a high level of corrosion resistance for use in the science classroom.
Here are some general guidelines for using this probe:
1.
The probe handle is constructed of molded plasticized Santoprene®. While this
material is very chemical resistant, we recommend that you avoid submerging the
probe beyond the stainless steel portion.
2.
Always wash the probe thoroughly after use.
3.
The probe can be left continuously in water at temperatures within the range of
–25° to 125°C. Continuous usage in saltwater will cause only minor discoloration of
the probe, with no negative effect on performance.
4.
You can leave the probe continuously in most organic compounds, such as
methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, n-hexane, lauric acid,
paradichlorobenzene, phenyl salicylate, and benzoic acid. The probe should not be
left in n-pentane for more than 1 hour.
5.
The probe can be left in strong basic solutions, such as NaOH, for up to 48 hours
with only minor discoloration. We do not recommend usage in basic solutions that
are greater than 3 M in concentration.
6.
The following chart provides the maximum length of time we recommend for
probe exposure to some common acids. Probes left in an acid longer than these
times may bubble and/or discolor, but will still be functional. We do not
recommend probes be left in
Acid
1 M HCI 20 minutes
2 M HCI 10 minutes
3 M HCI 5 minutes
1 M H2SO
2 M H2SO
12 CBL 2 Technical Reference
4
4
acid longer than 48 hours.
any
Maximum Exposure Time
48 hours
20 minutes
Acid
3 M H2SO
1 M HNO
2 M HNO
3 M HNO
1 M CH3CO OH 48 hours
2 M CH3CO OH 48 hours
3 M CH3CO OH 48 hours
1 M H3PO
2 M H3PO
3 M H3PO
7.
Cole Parmer has an extensive listing of chemical compatibility of grade 316 stainless
steel on their web site (
be used for general guidelines not covered in this summary.
4
3
3
3
4
4
4
www.coleparmer.com/techinfo
TI Temperature Sensor Note
Maximum Exposure Time
10 minutes
48 hours
48 hours
48 hours
48 hours
48 hours
48 hours
). This listing can
If a TI Temperature sensor (the flexible temperature sensor that came with the original
CBL) is used with CBL 2, it will auto-ID as the Stainless Steel Temperature sensor. Both
sensors use the same calibration that is built into the CBL 2.
TI Voltage Sensor
The TI voltage sensor is a generic sensor that you can use to read any voltage between
±10 Volts. The auto-ID resistor contained in the sensor causes the CBL 2 software to
automatically measure voltage. No conversion equation is loaded. The black hook
should be connected to ground and the red hook to the signal voltage.
Channels Connects to CH1, CH2, CH3 (analog channels)
Voltage range ±10 Volts
Chemical tolerance None (air only)
Pins used 1 Signal
2 Ground
4 auto-ID resistor
Note: It is very important that the ground connections of the analog inputs are never connected
to different potentials. These ground connections are all in common. Connecting the grounds to
different potentials may damage the CBL 2.
CBL 2 Technical Reference 13
1
1
Auto-ID Sensors
The CBL 2 contains provisions for the auto-ID sensor resistor values listed below. If
needed, a conversion equation is loaded automatically for some of the auto-ID values.
Channels 1, 2, and 3
IDENT
Valu e
2.2KThermocouple °CM200C to 1400¡C
33KTI Voltage sensorM10 to +10 Volts
6.8K Current sensor
3.3K Resistance sensor 1K to 100K
22K Extra long temperature sensor for °C
68K CO2 gas sensor (PPM) 0 to 5000 ppm
100K Oxygen gas sensor (PCT) 0 to 27%
150K C V voltage sensor (V)
220K C V current sensor (A)
10K Stainless steel or TI temperature sensor3 for °C
15K Stainless steel or TI temperature sensor for °F
4.7K TI Light sensor 0 to 1
1K Ex heart rate sensor (BPM) N/A
47K Voltage sensor 0 to 5 Volts
1.5K EKG N/A
Sensor Type
Range
2
M
10 to +10 Amps
J
L
50°C to 150°C
M
6 to +6 Volts
M
0.6 to +0.6 Amps
M25¡
C to 125¡C
M13¡
F to 257¡F
1
IDENT values are resistance values in ohms (tolerance ±5%).
2
Operation 3 is a mathematical conversion of voltage to a current reading (1V=1A).
There is no circuitry inside the CBL 2 unit to convert current to voltage; this must be
done in the external probe.
3
Default units for the Stainless Steel and TI Temperature sensors is °C.
Channel 11 (SONIC)
IDENT
Valu e
15K Motion detector, meters ½ meter to 6 meters
22K Motion detector, meters ½ meter to 6 meters
10K Motion detector, feet 1½ feet to 18 feet
33K Photogate sensor N/A
1
IDENT values are resistance values in ohms (tolerance ±5%).
14 CBL 2 Technical Reference
Sensor Type
Range
Custom Sensors
To create custom-designed sensors or other circuits for the analog input channels, the
sonic input channel, the digital input channel, or the digital output channel on the
CBL 2, you can purchase sensor kits from TI (
♦
For a custom analog sensor, use the Analog Probe Kit (order entry no. CBL/CA/D).
1-800-TI-CARES
Each sensor kit includes a four-foot length of telephone cable with a connector
attached to one end. The other end of the cable is not terminated.
♦
For a custom digital sensor, cut a CBR-to-CBL cable (order entry no. CBR/CA/C) into
two pieces to get two lengths of cable with connectors. (The digital probe kit used
with the original CBL will not work with CBL 2.)
♦
For a custom digital ID probe, contact Vernier Software and Technology
(
www.vernier.com
) for more information.
Be very careful when designing a custom sensor or circuit. For more accurate operation,
do not connect pins 1 and 6 together on the analog input channels. Pin 1 on the British
Telecom-style connector is the pin farthest from the release lever as shown in the
pictures below.
If you design a resistance-type sensor, connect pin 3 (Vres) to pin 6 (Vin-low) (refer to
“Connector Pinouts” below). Connect the resistance to be measured from the junction
of these pins to pin 2 (Gnd). The resistance range for useful measurements is limited
from approximately 1 Kohms to 100 Kohms.
) or its Instructional Dealers.
When the Operation parameter in Command 1 (page 23) is set to 2, 3, 5, 6, or 7, the
data is measured on the Vin pin (pin 1). The data for all other operations is measured
on the Vin-low pin (pin 6).
Note: The most current that can be drained from all three analog channels is 160 mA. This is
limited by the hardware.
CBL 2 Technical Reference 15
Connector Pinouts
The CBL 2 sensors use 6-pin British Telecom-style connectors.
Pin
1 Vin Echo DI0
2 Gnd Init DI1
3 Vres/Smart ID CLK Auto-ID DI2
4 Auto-ID +5 Volts DC +5 Volts DC
5 +5 Volts DC Gnd Gnd
6 Vin-low Not Applicable DI3
Channels: CH1, CH 2, CH 3 CH1, CH2, CH3
Input signal: Analog data Analog data
Analog CH1, CH2, CH3
(Right-hand Connector) (Left-hand Connector)
SONIC
Vin
DIG IN/OUT
Vin-low
Input range: ±10 Volts 0 to 5 Volts
Resolution (using CBL 2’s
10-bit A/D converter):
Input impedance: 1.046 M
Vres:
♦
♦
♦
♦
♦
♦
♦
Output reference voltage from the CBL 2 through a 15 Kohm resistor. When
using this feature, Vres should be tied to Vin-low and the value to be measured
should be connected between Vin-low and Gnd.
Gnd:
Ground (common for all channels).
Auto-ID: Auto-ID
pin 4 to ground.)
Echo:
Init:
Ultrasonic motion detector input.
Distance initialization signal
sensor detection data input. (
D0 In/Out to D3 In/Out:
Smart ID Clk:
Clock to synchronize data transfer from smart probes.
19.6 mV 5.6 mV
J
>10 M
Auto-ID
Input or output pins for digital pulses.
J
resistor connected from
16 CBL 2 Technical Reference
Programming the CBL 2
Digital Output Buffer
The digital output buffer (DOB) is a circular buffer that contains up to 32 elements. The
output from the buffer is 4-bits wide, and the outputs are CMOS (0-5V) compatible.
The data in Command 1 is entered as decimal representation of the digital value that is
output. For example, 0=0000, 5=0101, and 15=1111. At the beginning of each sample, a
pointer into the digital output buffer is incremented and the next available data is sent
to the output lines.
The electrical characteristics of the digital outputs are:
♦
Voutput-high ‚ 3.7V @ M400uA
♦
Voutput-low 0.65V @ 1.6mA
The number of times that the DOB outputs the contents of the buffer depends on the
number of data elements defined in Command 1 and the number of samples defined
in Command 3.
Digital Output Buffer Example
Command 1 list is {1,31,5,1,2,3,4,5}
where:
1=Channel Setup.
31=DIG OUT.
5=Five data elements.
1=0001 (digital nibble).
2=0010 (digital nibble).
3=0011 (digital nibble).
4=0100 (digital nibble).
5=0101 (digital nibble).
Command 3 list is {3,1,100}
where:
3=Sample and Trigger Setup.
1=One second sample time.
100=One hundred samples.
(Trigger Type defaults to manual
triggering.)
CBL 2 Technical Reference 17
The DOB outputs pulses that correspond to the five digital nibbles (1234512345...12345
etc.). This sequence is repeated 20 times (100 samples/5 data elements) to the DIG OUT
channel. The diagram below shows a portion of this output for the first five data
elements.
Sample
Clock
D3
D2
D1
D0
1234
1
5
Figure 1. Digital Output Example
Triggering and Thresholds
Two types of triggering thresholds can be set in the CBL 2:
♦
Hardware triggering
is set to trigger on a specific voltage level established by the
trigger threshold parameter.
♦
Software triggering
is set to begin data collection on either the rising edge or
falling edge of the signal, depending on the trigger type and trigger threshold
selected.
The THRESHOLD parameter specified in Command 3 can be used for two purposes:
♦
If the operation in Command 1 is frequency, period, or count (operation = 5, 6, or 7
on Channel 1 only), then the threshold parameter in Command 3 sets a voltage
level in the CBL 2 hardware. The signal on the Vin pin of CH 1 must pass through
this voltage for the CBL 2 to see the signal change states.
♦
If the operation in Command 1 is anything other than 5, 6, or 7, then the threshold
parameter in Command 3 specifies a trigger level and is measured in the units of
the sensor selected.
When triggering, sampling does not start until the signal on the trigger channel (also
specified in Command 3) passes through this level once in the direction specified. This
comparison of trigger level and signal level occurs in software, so any level in the
proper range can be selected. Also, either the Vin or VinLow pin (on any of the analog
channels or the sonic channel) can be used as the trigger channel. CBL 2 knows
whether to use the Vin or VinLow pin by looking at which operation was set up in
Command 1.
18 CBL 2 Technical Reference
0
1
2
3
T=
+
-
+
-
If a conversion equation is enabled for the trigger channel, then the threshold
specified in Command 3 should be a converted level. For example, if a pH probe is
plugged into CH 2 with a conversion equation loaded into CBL 2 and the trigger
channel specified as CH 2, the threshold level should be entered as a pH level in the
range 0-14, not as a voltage in the range 0-5V.
Measuring Period and Frequency
Period and frequency apply only to CH1 and only CH1 can be active if the operation is
set to 5 (Period) or 6 (Frequency). Period and frequency are measured on Vin pin (pin 1)
of CH1. Period and frequency measurements always use the hardware threshold.
The CBL 2 measures period and frequency by counting edges for 0.25 seconds, or by
measuring the time between the selected edges for one period—whichever is larger
(see figure below). If a significant number of edges are counted during the 0.25-second
period, the count is used to compute both period and frequency; otherwise, the period
and frequency are computed from the time interval for one period.
Figure 2. Period and Frequency Measurement
Trigger Type
2
3
4
5
Measuring Points
+ + (T=0 to 2)
N N
N + N
N N
(T=1 to 3)
(T=0 to 1)
+ (T=1 to 2)
The crossover point between the two computations is about 600 Hz. Because there can
be a one-count uncertainty during the 0.25-second period, the accuracy around 600 Hz
is approximately ±4 Hz (about 0.7%). The resolution of the timer measuring the time
between edges is 6.4 microseconds; therefore, the percentage accuracy improves for
frequencies above and below 600 Hz.
If the CBL 2 is set up using Command 3 to make multiple measurements at a particular
sample time, the CBL 2 waits for the sample time that you specified after it completes
the current measurement. It then initiates the next cycle of period/frequency
measurement. The minimum sampling time for period and frequency is 0.25 seconds.
Note: Period and frequency measurements using Trigger Type 4 or 5 are only possible on nonrepetitive signals or on repetitive signals that are less then 600 Hz. This is because at 600 Hz, the
edge counts will prevail.
CBL 2 Technical Reference 19
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