Applied Physics Systems 751 User manual

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MODEL 751
NATURAL GAMMA SENSOR
USER MANUAL
CONTACT US
HEADQUARTERS
425 Clyde Avenue Mountain View, CA 94043
OFFICE
650.965.0500
EMAIL
[email protected]m
APPLIEDPHYSICS.COM

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COPYRIGHT
Copyright 2014 - 2022 Applied Physics Systems Incorporated.
All Rights Reserved. The contents of this manual may not be reprinted in part or
whole without permission.
The contents of this manual are subject to change without notice.
TRADEMARKS
All other brands or products mentioned are trademarks or registered trademarks
of their respective holders and should be treated as such.
CONTACT INFORMATION
Applied Physics Systems
Corporate Headquarters
425 Clyde Avenue
Mountain View, California 94043 USA
Phone: [phone]
Email: [e-mail]
Web: www.appliedphysics.com
Technical Support Hours:
Monday - Friday
9:00 AM - 5:00 PM
Pacific Standard Time
DOCUMENT NUMBER
260-0222-03-0722

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REVISION HISTORY
Revision
Description
1
Initial Draft of this manual.
2
Removed reference to section 7.3 spreadsheet to calculate total
gamma correction factor.
3
New format
TABLE OF CONTENTS
MODEL 751.........................................................................................................................................................................1
NATURAL GAMMA SENSOR .................................................................................................................... 1
USER MANUAL..................................................................................................................................................................1
COPYRIGHT..................................................................................................................................................................... 2
TRADEMARKS................................................................................................................................................................. 2
CONTACT INFORMATION........................................................................................................................................ 2
DOCUMENT NUMBER................................................................................................................................................. 2
REVISION HISTORY...................................................................................................................................................... 3
1-INTRODUCTION......................................................................................................................................................5
2-SYSTEM SPECIFICATIONS................................................................................................................................6
3-MECHANICAL FEATURES .................................................................................................................................. 7
4-ELECTRICAL INTERFACE.............................................................................................................................................9
5-DATA INTERFACE.................................................................................................................................................10
6-MODEL 751 GAMMA SENSOR COMMANDS............................................................................................11
6.1 –MODEL 751 SYSTEM BINARY DATA REQUEST COMMANDS........................................................12
6.1.1 -ID COMMAND (KEYBOARD COMMAND 0, 0X30 HEX)...............................................................12
6.1.2 -BINARY COUNT COMMAND (KEYBOARD COMMAND 1, 0X31 HEX) ...................................13
6.1.3 -BINARY RATE COMMAND (KEYBOARD COMMAND 2, 0X32 HEX) ......................................14
6.1.4 -BINARY TRANSMISSION DECODING CONVENTION...................................................................15
6.2 –MODEL 751 SYSTEM ASCII DATA REQUEST COMMANDS...........................................................15
6.2.1 -ASCII RATE COMMAND (KEYBOARD COMMAND 6, 0X36 HEX)......................................... 16
6.2.2 -ASCII ACCELEROMETER COMMAND (KEYBOARD COMMAND 7, 0X37 HEX) ............. 16
6.2.3 -ASCII SEND 751 CONFIG DATA COMMAND (KEYBOARD COMMAND R, 0X72 HEX) 17
6.3 -MODEL 751 CONFIGURATION COMMANDS......................................................................................18
7-CORRECTIONS TO THE GAMMA COUNT RATE FOR USE IN MWD SYSTEMS ........................19

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7.1 -PRESSURE BARREL CORRECTION (PB CORRECTION)................................................................. 20
7.2 -DRILL COLLAR AND DRILLING FLUID CORRECTION (CM CORRECTION) ............................21
8-NET SYSTEMS........................................................................................................................................................23
8.1 -NET PACKET DESCRIPTION........................................................................................................................ 24
8.2 -NET PROTOCOL.............................................................................................................................................. 25
8.3 -THE CRC PROGRAM..................................................................................................................................... 26
A-MODEL 751 CONFIGURATION COMMAND REFERENCE ................................................................ 28
Tables
TABLES
Table 1. Model 751 Gamma Sensor Specifications.............................................................................6
Table 2. Model 751 Electrical Interface........................................................................................................9
Table 3. Model 751 Data Request Commands......................................................................................11
Table 4. ID Command Format Example Key.........................................................................................13
Table 5. Binary Count Command Format Example Key...............................................................13
Table 6. Rate Command Format Example Key...................................................................................14
Table 7. Model 751 Send Command Format Example Key..........................................................17
Table 8. Model 751 Operation Configuration Commands...........................................................18
Table 9. NET Packet Key..................................................................................................................................... 24
Table 10. NET Directional Sensor Command Key ............................................................................. 26
Table 11. Model 751 Configuration Commands.................................................................................. 28
FIGURES
Figure 1. Model 751 Main Connector ............................................................................................................. 7
Figure 2. Model 751 Mating Connector.......................................................................................................8
Figure 3. Model 751 Sensor Assembly Drawing.....................................................................................8
Figure 4. Model 751 Wiring Diagram.............................................................................................................9
Figure 5. Pressure Barrel Correction Factors in Inches................................................................ 20
Figure 6. Pressure Barrel Correction Factors in Centimeters ....................................................21

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1 - INTRODUCTION
The Applied Physics Systems Model 751 Gamma Sensor is designed to measure
the background gamma radiation occurring in well bores. This sensor is used
mainly to detect the presence of porous petroleum reservoirs (such as
sandstones and limestones), which are generally less radioactive than nonporous
strata (such as shales).
The Model 751 gamma sensor can be used as either a standalone system or in
conjunction with Model 750, 760, or 850 directional sensors:
• When used as a standalone system, communication with the Model 751
gamma sensor is by means of a bi-directional serial port operating at TTL
logic levels. An ASCII command language is used to send commands to
the Model 751 and data from the Model 751 is sent out in ASCII format.
• When the Model 751 is used in conjunction with a Model 750, 760, or 850
directional sensor, a NET interface is used for communication. For the NET
configuration, data from the Model 751 gamma sensor is continually
requested by the directional sensor and is combined with directional data
and transmitted out the directional sensor’s main serial data interface.
To achieve high gamma sensitivity, a 1-inch diameter by 5-inch long scintillation
crystal is used to detect gamma rays. Scintillation light flashes caused by
individual gammas are amplified by using a photo multiplier tube that outputs a
short pulse for each gamma detected. Pulses are further amplified and counted
by a microprocessor system that also handles communication with external
devices.
The Model 751 system also has two 50-gee vibration sensors (accelerometers),
which can be used to monitor drilling induced vibration and shock. The two
vibration sensors are oriented to measure axial and transverse shock and
vibration.

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2 - SYSTEM SPECIFICATIONS
This section describes the system specification for the Model 751 Gamma Sensor.
Table 1. Model 751 Gamma Sensor Specifications
Electrical
Input Voltage Range
+15 V to +30 V
Current Draw
90 mA @ 15 V, 45 mA @ 30 V
Power Requirements
1.5 W (max)
Logic Level
TTL
Baud Rate
User Programmable up to 9600 baud
Protocol
User selectable, ASCII or Binary
Environmental
Operating Temperature Range
0°C to 150°C
Storage Temperature Range
-25°C to +160°C
Shock
1000 G1ms half sine wave
Vibration (random)
10 Grms, 50-250Hz
Performance
Accuracy
± 5%
Thin-bed Resolution
6" (236 mm) in an 8” diameter hole
Range
0 - 511 API counts/second (30 second intervals)
Vibration and Shock Detection
2 axis ± 50 gee 400 Hz
Physical
Outside Diameter (O.D.)
1.375” (35 mm)
Length
approximately 18.3” (464.8 mm),
depending upon connector configuration
Weight
1.95 lbs (884.5 grams)
Scintillation Crystal
1" dia. (25.4 mm) and 5" (127 mm) in length,
mounted in Stainless Steel Case
Photomultiplier Tube
Hamamatsu Model 3991A
Main Connector
MDM9PH003P (ITT Cannon)
Mating Connector
MDM9SH003L (ITT Cannon)

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3 - MECHANICAL FEATURES
A drawing of the Model 751 Sensor is shown in Figure 1. When used in pulser or EM
MWD systems, usually the Model 751 is mechanically connected directly to a
Model 750, 760, or 850 directional sensor and mounted in a cylindrical pressure
barrel. An overlap mechanical connection using four 8-32 stainless steel screws is
used to attach the Model 751 to the directional sensor.
When the Model 751 is mechanically mated to the directional sensor, electrical
connection is also made via a 9-pin MDM connector mounted in the overlap
recess. This connector is float-mounted to reduce vibration-induced damage
that can occur in drilling applications.
The photographs below show the connectors in more detail:
Figure 1. Model 751 Main Connector

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The drawing below is an assembly drawing of a Model 751 gamma sensor.
Figure 3. Model 751 Sensor Assembly Drawing
Figure 2. Model 751 Mating Connector

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4 - Electrical Interface
The electrical connections for the Model 751 Gamma Sensor are shown in the
wiring diagram below, and in Table 2.
Table 2. Model 751 Electrical Interface
MDM Pin
Function
1
Serial (TTL level) from gamma
2
Serial (TTL level) to gamma
3
Voltage
4
Ground
Remaining pins
Not used
Communication with the Model 751 is accomplished via the TTL-level serial
communications lines. The Model 751 can be connected to a PC for testing if a
TTL-to-RS232 conversion box is inserted in the communication lines between the
Model 751 and PC. TTL-to-RS232 conversion systems can be supplied by Applied
Physics Systems or other vendors.
Figure 4. Model 751 Wiring Diagram

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5 - DATA INTERFACE
Commands are sent to the Model 751 as ASCII characters at the default baud rate
of 9600 using 8-bit data words with one stop bit and no parity bit.
An easy method of communicating with the Model 751 is to use a PC running a
terminal emulator program such as Windows HyperTerminal or ProComm. When
these programs are used, any typed commands are sent out the specified COM
port and any data received from the Model 751 system are displayed on the PC
display device.
When using a terminal emulator, the emulator program must be configured for
direct connect to a COM port on the PC and the following settings should be used:
• baud rate = 9600
• data word = 8-bits
• no parity
• stop bits = 1
• handshaking option = none
All commands to the Model 751 are invoked by multi byte sequences in which the
first byte is always a command token hex 06 (0x06). The bytes following the token
define the command being sent. Commands sent to the 751 system are of two
general types:
• Binary and ASCII data requests
• System configuration commands
ASCII data transmitted from the 751 sensor is formatted to be easily displayed on
a computer monitor. Binary data is transmitted from the 751 sensor in a data
packet with the following structure:
<Token> <Command> <data1> <data2>…<dataN> <CRCL> <CRCH> <token> <Eot>
Where:
• <Token> = 0x06,
• <CRCL><CRCH> is a two byte CRC, and
• <EOT> = (0x06)(0x04) and denotes the end of the packet.

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If the token occurs within the requested data sequence it is replaced with two
tokens. Multi-byte binary numbers in the requested data sequence are returned
highest byte first, then next highest, with the least significant byte last. To send the
command token using a computer keyboard hold down the control key and type
the letter f.
The gamma sensor includes two accelerometers one which measures transverse
and one which measure axial shock. Both accelerometers have a full scale equal
to ±50g. The reported data from the accelerometers is calibrated to read in gees.
The 751 system also has a temperature sensor. Data reported from the
temperature sensor is calibrated to read in degrees centigrade.
6 - MODEL 751 GAMMA SENSOR
COMMANDS
This section describes the two types of Model 751 gamma sensor commands:
• Binary data request commands
• ASCII data request commands
• Configuration commands
To send a data request command to the 751 system, enter the command token
<Ctrl/F>
(pressing the Ctrl key and the f key simultaneously) followed by one of the
keyboard commands listed in Table 3. Press Enter to send the command.
The data request commands are listed in the table below:
Table 3. Model 751 Data Request Commands
Keyboard
Command
Hex Command
Command Result
0
0x30
Send 751 identity data
(see Section 6.1.1 for more information)
1
0x31
Send binary count data in binary
format

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(see Section 6.1.2 for more information)
2
0x32
Send Gamma rate data in binary
format
(see Section 6.1.3 for more
information)
6
0x36
Send gamma data in ASCII format
(see Section 6.2.1 for more information)
7
0x37
Send accelerometer data in ASCII
format
(see Section 6.2.2 for more
information)
r
0x72
Send 751 configuration data
(see Section 6.2.3 for more
information)
t
0x74
Send temperature data
!
0x21
Send software version
6.1 – MODEL 751 SYSTEM BINARY DATA
REQUEST COMMANDS
This section describes the binary commands (keyboard commands 0, 1, and 2) in
Table 3.
6.1.1 - ID COMMAND (KEYBOARD
COMMAND 0, 0x30 HEX)
The data in this command is the ASCII string "01Gamma 004" which identifies the
unit.
Example of a 0x30 response:
06 30 30 31 47 61 6D 61 20 30 30 34 0A 58 A7 06 04
Table 4 explains the contents of this sample data response packet.

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Table 4. ID Command Format Example Key
Contents
Description
06 30
Header is the token and echoed command
30-61
This sequence spells out 01Gamma
20
ASCII space
30 30 34
This sequence spells out 004
0A
ASCII line feed
58 A7
16-bit CRC
06 04
EOT sequence
6.1.2 - BINARY COUNT COMMAND
(KEYBOARD COMMAND 1, 0x31 HEX)
This command returns gamma count information in the form of an elapsed time
and count total since receipt of the last command of this type. The time and
count are 32-bit integers, with the most significant byte first. The count data is
followed by the two single bytes representing the maximum accelerations
(shock) recorded since receipt of the last command. The acceleration values are
calibrated to read in Gees. The 0x31 command (for a description of the NET
command, see Section 8) is the command that is used to acquire gamma data in
the APS EM MWD and APS YYY Pulser MWD systems.
Example of a 0x31 response:
06 31 00 02 57 AD 00 00 01 D2 01 01 BB 19 06 04
The table below explains the contents of this response:
Table 5. Binary Count Command Format Example Key
Contents
Description
06 31
Header is the token and retransmitted command
00 02 57 AD
The time period in units of 96 µS. Because 00 02 57 AD hex
is equivalent to
153517 decimal, the time period is (153517)*(96e-06) =14.74
seconds

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00 00 01 D2
The count. 00 00 01 D2 Hex = 466 Decimal, so the rate is
466/14.74=31.61
Counts/sec.
01 01
Two maximum accelerations recorded since receipt of the
last command. Maxi-
mum transverse shock = 6 Gee and maximum axial shock
= 2 Gee
BB 19
16-bit CRC
06 04
EOT sequence
The command resets the count values and starts new collection cycle. The
collection continues to accumulate until another read command is issued. The
longer time period between the read times allows for better averaging.
6.1.3 - BINARY RATE COMMAND
(KEYBOARD COMMAND 2, 0x32 HEX)
This command is useful because it returns the count rate directly. The sample
period can be set to 3 or 6 seconds by using the cs3 and cs6 configuration
commands or set to a user defined time by using the wa command (see Section
6.3 for an explanation of these commands). An example of the binary command
response when the sample period is 6 seconds is given below:
06 32 00 A1 01 01 A9 AD 06 04
The table below explains the contents:
Table 6. Rate Command Format Example Key
Contents
Description
06 32
Header is the token and retransmitted
command
00 A1
The rate = 161 decimal. The rate in counts per
second is
(161/6.29) = 25.6 counts/sec.
01 01
Two accelerations

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A9 AD
16-bit CRC
06 04
EOT sequence
6.1.4 - BINARY TRANSMISSION DECODING
CONVENTION
If a command token (0x06) occurs in the sensor data information, it is replaced
by (0x06)(0x06).This is to distinguish it from an end of packet or start of packet
indicator. For example, if a net sensor has the following data to send:
<0x01> <0x73> <0x06> <0x19> <0x06> <0x06> <0x56>
The actual transmitted data would be as follows:
<0x01> <0x73> <0x06> <0x06> <0x19> <0x06> <0x06>> <0x06> <0x06> <0x56>
Note that the double token becomes four tokens, each pair in the transmitted
string representing one real data byte in the original message.
The CRC calculation begins with the command byte, and ends with the last data
byte. When a token (0x06) occurs in the original data, it is only included once in
the checksum calculation. If a token byte should occur in the checksum it is
expanded to two tokens, but the checksum is otherwise unchanged. If the low
byte of the CRC is 0x06 (<Token>) then there will be three <Token>s in a row. Two
<Token>s result from expanding the <Token> in the CRC and the third represents
the “real” token which indicates the end of the packet.
6.2 – MODEL 751 SYSTEM ASCII DATA
REQUEST COMMANDS
This section describes the ASCII commands (keyboard commands 6, 7, r, and so
on) in Table 3. Model 751 Data Request Commands.

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6.2.1 - ASCII RATE COMMAND (KEYBOARD
COMMAND 6, 0x36 HEX)
The ASCII command (0x36) returns the gamma count rate in the following format:
Time 106306 Counts=273
Rate= 26.8 cps
T= +26.37
The time number in the above example is in increments of 96 microseconds. This
is equivalent to 106306 x 96µS = 10.2 sec. The gamma count in the above example
is 273 so the rate is 273/10.2=26.8 cps. When the ASCII rate command is received
the 751 sensor responds by sending the time and number of counts since the last
ASCII rate command. The time and count values are then zeroed so that time and
count accumulation can restart. The temperature of the system (+26.37) is also
included in the ASCII rate response.
6.2.2 - ASCII ACCELEROMETER COMMAND
(KEYBOARD COMMAND 7, 0x37 HEX)
The ASCII command (0x37) reports the maximal transverse and axial shock and
vibration levels and has the format:
Axial Shock Max = 2 gee
Transverse Shock Max = 6 gee
Axial Vib RMS = 2.0 gee
Transverse Vic RMS = 1.1 gee
The maximum shock values are those values observed since the receipt of the
last 0x37 command. The RMS vibration values are calculated over a time period
equal to the last gamma count interval. Shock and vibration are sampled at a
data rate of 250 samples per second.

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6.2.3 - ASCII SEND 751 CONFIG DATA
COMMAND (KEYBOARD COMMAND R, 0x72
HEX)
The ASCII command (0x72) response has the following format:
APS SNG0001 APS Gamma 3.27.01
Autosend Delay: 100 ms
Acquisition Period: 6 seconds
DarkCurrent:+0.000 APICal:+1.00000
Temperature Corrected APICal:+1.00000
Tstart:+180.000 T_X2:+0.00002500 T_X1:-0.00350000
T_X0:+1.07000005
TempScale(degree/count):+0.12130 TempOffset(degree c):+273.0
Cal:+25.0
Pulseout mode: Uncorrected
The table below explains the contents:
Table 7. Model 751 Send Command Format Example Key
Contents
Description
APS SNG0001 APS
Gamma
Gamma serial number
Autosend Delay
Autosend inter-packet delay time
Acquisition Period
Gamma count acquisition time
DarkCurrent,
Tempera- ture
Corrected, Tstart,
Tempscale
751 API calibration and temperature calibration data. The
API calibration factor enables the gamma count output to
be adjusted to the absolute API standard.
Pulseout
Pulseout notation refers to a gamma factory test mode

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6.3 - MODEL 751 CONFIGURATION
COMMANDS
To write a configuration command, enter:
<Ctrl/F>
(pressing the Ctrl key and the f key simultaneously) followed by one of the
keyboard commands listed in Table 8. Press Enter to send the command.
For example, to set the system to autosend ASCII data, type:
<Ctrl/F> ca1
and press the Enter key.
The Model 751 system has 22 configuration commands. Many of these commands
should only be used during the calibration of the Model 751 system. See Appendix
A - MODEL 751 CONFIGURATION COMMAND REFERENCE for a complete list of
configuration commands. The table below contains the configuration commands
used to configure the operating characteristics of the Model 751 system:
Table 8. Model 751 Operation Configuration Commands
Keyboard
Command
Command Result
c h
Display the help menu for c-type commands
c b x
Start (x=1) or stop (x=0) binary autosend
c a x
Stop (x=1) or stop (x=0) ASCII autosend
c r 1200
Set baud rate to 1200
c r 2400
Set baud rate to 2400
c r 9600
Set baud rate to 9600
c s 3
Set gamma count time to 3 seconds
c s 6
Set gamma count time to 6 seconds
c o
Zero accelerometer output
w h
Display the help menu for w-type commands
w a ##
Set gamma count time to ## seconds
w s ####
Sets the inter packet delay for autosend mode to ####
milliseconds

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The Model 751 system has two autosend data modes:
• ASCII autosend
• Binary autosend
These autosend modes are started and stopped by sending commands as listed
in Table 8 above. The format of the data transmissions in autosend mode is the
same as that described for the Binary or ASCII Rate command (Section 6.1.3 and
Section 6.2.1, respectively). The data acquisition time period used in the autosend
modes is set using the cs3, cs6, and wa## commands.If the data transmission
rate is set to be shorter than the data acquisition time, the data sent will not
change until the data acquisition time has finished.
7 - CORRECTIONS TO THE GAMMA COUNT
RATE FOR USE IN MWD SYSTEMS
When the 751 sensor is used in drilling applications it is generally mounted in a
beryllium copper pressure vessel and deployed in a (usually nonmagnetic) drill
collar. In addition, drilling fluids (“drilling mud”) is present in the borehole being
drilled. These factors tend to reduce the count rate recorded by the 751 sensor
from the true borehole formation count rate. The true borehole count rate must be
determined; to do so, correct the Model 751 count rate for the following factors:
• Pressure barrel density and thickness
• Drilling fluid density and thickness
• Drill collar density and thickness
The three correction factors should be multiplied together to determine the total
overall correction factor. It is not uncommon for total correction factors to be 5 or
greater. Generally, the drill collar will produce the largest correction factor. These
correction factors are described in more detail below.

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7.1 - PRESSURE BARREL CORRECTION (PB
CORRECTION)
The following two graphs show pressure barrel correction factors using inch and
centimeter units.
Figure 5. Pressure Barrel Correction Factors in Inches