Group3 DTM-151 User manual

01 April 2010
Group3 Technology Limited
2 Charann Place, Avondale, Auckland 1026
P.O. Box 71-111, Rosebank, Auckland 1348, New Zealand.
Phone: [phone] Fax: [phone]
email: [e-mail]
web: www.group3technology.com
DTM-151
DIGITAL TESLAMETER
with serial communications
V7.1
USER’S MANUAL

Thank you for purchasing and using a Group3 digital teslameter. We hope you will join the many hundreds of users
worldwide who are enthusiastic about our products.
Group3 has been designing and building magnetic field measuring equipment since 1983. We are constantly upgrading
our products and support documentation. We welcome input from our customers, so if there are aspects of the
instrument which you particularly like, or which you would like to see improved, please contact your Group3
supplier (see back page for a complete list) or Group3 directly with your suggestions to [e-mail].
The Group3 website, www.group3technology.com contains details of all our products.
This site is regularly updated, so check it from time to time to learn about recent
developments.

CONTENTS
1. General Description 1-1
2. Specifications of DTM-151 System 2-1
3. Setting Up
3.1 Introduction 3-1
3.2 Connecting the Hall Probe 3-1
3.3 Connecting the Power Source 3-2
3.4 Fiber Optic Connections 3-4
3.5 Electrical Serial Data Input/Output Connections 3-4
3.6 Internal DIP Switch Settings 3-9
3.7 Bit Rate Selection 3-12
3.8 Second Watchdog Operation 3-13
3.9 Analog Outputs 3-15
3.10 Grounding 3-16
3.11Installing the Panel Mount Option 3-17
3.12Installation Techniques for Electrically Noisy Environments 3-18
4. Operating Instructions
4.1 Zeroing 4-1
4.2 Installing the Probe 4-2
4.3 Reading the Field Value 4-3
4.4 Display Modes, Using the Front Panel Keys 4-4
4.5 Using the Serial Data Inputs & Outputs 4-7
4.6 Digital Filtering 4-14
4.7 Triggered Operation 4-15
5. Technical Diagrams
General Information 5-1
Display Board Schematic 5-2
Display Board Component Overlay 5-3
Display Board Parts List 5-3
Probe Plug Board Schematic 5-4
Probe Plug Board Component Overlay 5-5
Probe Plug Board Parts List 5-5
Processor Board Schematic 5-6
Processor Board Component Overlay 5-7
Processor Board Parts List 5-8
Analog Board Schematic 5-9,10
Analog Board Component Overlay 5-11
Analog Board Parts List 5-12,13
DTM-151 (serial) User’s Manual Contents-1

LIST OF FIGURES
Fig. 1 Power Input Connections of the -L option 3-3
Fig. 2 RS-232-C Connector & Jumper Locations 3-6
Fig. 3 Send and Receive Jumpers 3-8
Fig. 4 Option Jumpers 3-8
Fig. 5 Location of Processor Board Switches 3-10
Fig. 6 Location of Second Watchdog Select Jumper 3-13
Fig. 7 Panel Cutout Dimensions 3-17
Fig. 8 Probe Dimensions 4-3
Fig. 9 G3CL - Alternative Configurations 4-8
Display Board Schematic 5-2
Display Board Component Overlay 5-3
Display Board Parts List 5-3
Probe Plug Board Schematic 5-4
Probe Plug Board Component Overlay 5-5
Probe Plug Board Parts List 5-5
Processor Board Schematic 5-6
Processor Board Component Overlay 5-7
Processor Board Parts List 5-8
Analog Board Schematic 5-9,10
Analog Board Component Overlay 5-11
Analog Board Parts List 5-12,13
LIST OF TABLES
Table 1 G3CL Connector Pin Assignments 3-5
Table 2 RS-232-C Connector Pin Assignments, Terminal Mode 3-7
Table 3 RS-232-C Connector Pin Assignments, Modem Mode 3-7
Table 4 DIP Switch Functions 3-10
Table 5 Serial Data Format Switch Settings 3-11
Table 6 String Terminator Switch Settings 3-11
Table 7 Bit Rate Switch Settings 3-12
Table 8 Analog Output Connector Pin Assignments 3-15
Table 9 DTM Serial Commands 4-9
Contents-2 DTM-151 (serial) User’s Manual

1 GENERAL DESCRIPTION
The DTM-151-_S Digital Teslameters offer accurate, high resolution measurement of magnetic flux densities, with
direct digital readout in tesla or gauss, and serial communications by fiber optics or RS-232C for system applications.
The instruments are light and compact, and the probes are easy to use. The DTM-151 has been engineered to withstand
the severe electrical interference produced by high voltage discharge.
This description includes features of the IEEE-488 interface option which is an alternative to the serial communication
option. If your teslameter is the IEEE-488 version, refer to the DTM-151-_G User's Manual.
FEATURES
Measures magnetic fields over four ranges up to 3 tesla with polarity indication; resolution up to 1 part in 600,000.
Used with special miniature Hall probe - easy to attach to magnet pole or other hardware. Probe holders are available
as optional accessories.
Accuracy and temperature specifications include total system performance, probe and instrument. This is the only
meaningful indication of measurement accuracy.
Probe is calibrated, with field and temperature characteristics stored in memory chip contained in cable plug.
Basic accuracy 0.01% of reading + 0.006% of full scale.
Microprocessor reads probe calibration data stored in probe connector and computes corrected field reading.
Temperature coefficient 10ppm/°C overall achieved using temperature sensor in probe.
Microprocessor calculates corrected field reading.
Accuracy is verified against nuclear magnetic resonance (NMR) standard.
Probe calibration is verified at many field points, and a printed calibration table is
supplied with every probe.
AC mode measures and displays time-varying fields between 8 Hz and 3000 Hz.
Front panel keys set the display to read the desired field range, to read the peak value of the field using the peak hold
function, to show the ac field component, and to display the probe temperature.
Peak hold is implemented digitally, has zero sag.
DTM-151 (serial) User’s Manual 1-1

Digital filtering of the displayed field reading suppresses short-term fluctuations. The filtering characteristic is non-
linear; small field variations within a narrow window-centered on the currently displayed value are filtered; large field
changes are displayed immediately. Filter window and time-constant may be changed by remote command.
Filtering is controlled by an internal switch.
Two digital communication options: either serial (RS-232C and fiber optic) or IEEE-488 General Purpose Interface Bus.
With the serial option, a single teslameter may be connected to standard RS-232C equipment, or up to 31 units may be
interconnected on a Group3 Communication Loop (G3CL) and driven from computer or terminal.
Fiber optic ports duplicate functions of RS-232C signals, for electrical noise immunity and voltage isolation. Fiber optic
links may be up to 60 meters in length, using Hewlett-Packard HFBR-3500 series fiber optic cables. Use a Group3 fiber
optic repeater (FOR) to extend communication distance.
The IEEE-488 option fully supports all relevant GPIB functions and commands, including full talker-listener capability,
serial and parallel polling, service request, and talker-only.
ASCII control commands are accepted to modify the output data format, to change the rate of data transmission or to
request transmission of a single field reading. Other commands set scaling and offset, select the field range, select ac
and peak hold functions, turn on and off digital filtering and modify the filter characteristics. System status may be
determined remotely.
The system can be operated in triggered mode where field measurements by one or more teslameters are triggered in
synchronism with each other by external command.
Internal switches select serial data format and baud rate, device address, string terminators, filtering, field units in
gauss or tesla, data format, service request action, EOI action, and perform system reset.
Two analog outputs are available: instantaneous field value (0 to 3 kHz), rectified time-varying (ac) component of field,
(8 Hz to 3 kHz).
All model variations are available without display and keys for true 'black box' magnetic-field-to-computer interfacing.
A panel mount model with display is available.
1-2 DTM-151 (serial) User’s Manual

2 SPECIFICATIONS OF DTM-151 SYSTEM
Specifications include LPT-141 or MPT-141 Hall Probe.
Measurements field value and time-varying (ac) component of field
Field ranges 0.3 0.6 1.2 3.0 tesla full-scale,
3 6 12 30 kilogauss full-scale,
with polarity indication
maximum calibration field ±2.2 tesla, ±22 kilogauss
Resolution DC mode with digital filtering ON:
1 in 600,000 of bipolar span as shown on front panel display.
range display resolution serial/GPIB resolution
gauss tesla gauss tesla
0.3 tesla 0.01 0.000001 0.001 0.0000001
0.6 tesla 0.02 0.000002 0.01 0.000001
1.2 tesla 0.04 0.000004 0.01 0.000001
3.0 tesla 0.10. 00001 0.01 0.000001
Resolution DC mode with digital filtering OFF, and AC mode:
1 in 120,000 of bipolar full-scale span in display:
range display resolutionserial/GPIB resolution
gauss tesla gauss tesla
0.3 tesla 0.05 0.000005 0.001 0.0000001
0.6 tesla 0.1 0.00001 0.01 0.000001
1.2 tesla 0.2 0.00002 0.01 0.000001
3.0 tesla 0.5 0.00005 0.01 0.000001
20-bit digitising of field reading.
Accuracy DTM-151 with LPT-141 or MPT-141 probe:
±0.01% of reading ±0.006% of full-scale max. at 25°C
Temperature DTM-151 with LPT-141 or MPT-141 probe:
Stability calibration: ±10 ppm of reading/°C max.
zero drift: ±(1 microtesla + 0.0003% of full-scale)/°C max.
add -3ppm/°C for each meter of probe cable
Time stability ±0.1% max. over 1 year
DTM-151 (serial) User’s Manual 2-1

Measurement rate 10 measurements per second
Response time Full-scale change of displayed field reading settles to within
resolution in less than 0.3 second (filtering off - see below)
Peak hold mode Displays maximum field since mode entered or reset.
Peak hold is implemented digitally with zero sag or decay.
AC mode Displays time-varying (ac) component of field;
frequency response: 8 Hz to 3 kHz at -3dB points.
response time-constant: 0.2 seconds.
average responding,
reads rms value of sinusoidally-varying field.
reading is not linearity or temperature corrected.
Display 7-character 7-segment alphanumeric display.
Indicators 8 back-lit legends for:
0.3 0.6 1.2 3.0 tesla range selected,
peak hold mode on, digital filtering on, tesla/gauss field units.
Display modes magnetic field, peak hold field, ac field, peak ac field
Digital filtering field value filtering smoothen out small fluctuations in the reading;
large, rapid field changes are not filtered;
internally switch selected.
Keys 2 keys for range selection, access to display modes,
zeroing field display, peak hold reset.
Digital interfacing serial option: RS-232C and fiber optic.
parallel option: IEEE-488 General Purpose Interface Bus.
Digital data format ASCII input commands and output responses.
Commands requests for field values,
setting and inspection of display and control modes,
field measurement triggering, entry of numerical values,
setting units, output data format, and filter characteristics,
test commands.
Output responses field value in tesla or gauss followed by optional T or G
and string terminator(s), system status,
numerical data requested by commands, messages.
2-2 DTM-151 (serial) User’s Manual

Serial bit rate 16 rates, switch selected, 50, 110, 134.5, 150, 200, 300, 600,
900, 1050, 1200, 1800, 2000, 2400, 4800, 9600, 19200baud.
System orientation Group3 Communication Loop (G3CL) using serial ports,
simple loop for 31 devices, no multiplexer required;
GPIB with IEEE-488 option.
Fiber optic cable Hewlett-Packard HFBR-3500, 60 meters max.
Fiber optic repeater available for extended communications.
On-board switches serial baud bit rate selection, load defaults, device address,
filtering, string terminators, data format,
service request enable, EOI enable.
Analog outputs dc output - instantaneous field analog:
full-scale output: ±3V nominal
source impedance: 1000Ω
accuracy: ±10%
bandwidth: 3kHz at -3dB, rolloff 3-pole 60dB/decade
ac output - rectified analog of time-varying (ac) field:
frequency response: 8Hz to 3kHz at -3dB points
time-constant: 0.2 seconds
average responding, delivers rms value of sinusoidal field
full-scale output: 3V nominal
source impedance: 1000Ω
accuracy: ±12%
IEEE-488 functions SH1 source handshake capability
AH1 acceptor handshake capability
T5 talker (basic talker, serial poll, talk-only mode,
unaddressed to talk if addressed to listen)
TE0 no address extension talker capability
L4 listener (basic listener, unaddressed to listen if addressed to talk)
LE0 no address extension listener capability
SR1 service request capability
RL0 no remote local capability
PP1 parallel poll capability (configured by controller)
DC1 device clear capability
DT1 device trigger capability
C0 no controller capability
GPIB connector standard Amphenol 57-20240 with metric standoffs
DTM-151 (serial) User’s Manual 2-3

Memory back-up user-entered data storage for 30 days with power off.
Power source ac: min 8V at 0.7Arms, max 15V at 0.4Arms
dc: min 9V at 0.5A, max 19V at 0.25A
ac line input plugpack supplied.
Power fuse on processor board: 1 amp antisurge 5 x 20mm
To obtain maximum spark protection, use PS12D7 power
supply and ferrite kit 11000036. See section 3.12.
L option: 115/208/230 V ac power input.
Enclosure aluminium, 217 x 125 x 50 mm, textured finish,
light tan colour, tilt stand fitted to bench models.
Ambient field Maximum operating field for instrument:
10 millitesla with single-range probe,
0.5 millitesla with multi-range probe.
Temperature range 0 to 50°C operating, absolute maximum temperature of probe 60°C.
Instrument weight 1.2 kg, shipping weight 2.5 kg.
Probes LPT series, transverse types,
sensitive area 4 x 1.6mm,
probe head size:
LPT-141 and LPT-231: 14 x 14 x 2.5 mm
MPT series, miniature transverse types,
sensitive area 1.0 x 0.5mm,
probe head size:
MPT-132 MPT-230 MPT-141 MPT-231: 14 x 5 x 2 mm
Standard cable length: 2 meters.
Special cable lengths to 30 meters.
Probe cable is shielded.
2-4 DTM-151 (serial) User’s Manual

ORDER CODES
Basic teslameters,
capable of four measurement ranges 0.3, 0.6, 1.2, 3.0 tesla full scale,
support all LPT and MPT series probes, plugpack supplied except for option -L.
DTM-151 (supports LPT-141, LPT-231, MPT-141, MPT-231 probes)
Options
Bench style instrument with display: add suffix –D|
Panel-mount version: add suffix –P| one of these options
Without display, plugpack powered: add suffix –N| must be specified
Without display, line voltage power: add suffix –L|
Serial data input/output, RS-232C & fiber optic: add suffix S| must select
IEEE-488 GPIB capability: add suffix G| one option
Example: DTM-151-DS
Probes
Four ranges, standard 2 meter shielded cable
LPT-141-2s | standard sensitivity LPT-231-2s | high sensitivity
MPT-141-2s | probes MPT-231-2s | probes
Single range probes: add range suffix -03, -06, -12, -30.
Special probe cable lengths: change length suffix to -Xs,
where X is the desired cable length in meters, 30 max.
Example: LPT-141-10s for 10 meter cable
Accessories
fiber optic cable fitted with connectors, 60 meter length maximum.
probe holders.
fiber optic repeater, bidirectional, model FOR-2PP.
fiber optic to RS-232C adaptor, model FTR.
digital display for remote control & readout of field values, model DPM.
rack panels, 3.5 inches high (2U), for rack mounting 1, 2, or 3 DTMs or DPMs.
ferrite kit 11000036 for spark protection.
power supply PS12D7 for spark protection.
DTM-151 (serial) User’s Manual 2-5

2-6 DTM-151 (serial) User’s Manual

3 SETTING UP
3.1 INTRODUCTION
This manual provides operating instructions for all members of the DTM-151 family of digital teslameters with
serial communications, and their companion LPT-141, LPT-231, MPT-141, and MPT-231 series Hall probes.
For a summary of all current members of the product family, see page 2-5. These instructions are written for
a teslameter with front panel display and keys, DTM-151-DS/PS. Users of teslameters without display and
keys should ignore sections of this manual referring to these features. All other aspects of operation are
identical. Before using your teslameter for the first time, please read through sections 3.2, 3.3, 4.1, 4.2, and
4.3 of this manual. This will give a quick introduction to basic operation of the instrument. If you have a
teslameter without display, DTM-151-NS/LS, also read sections 3.4, 3.5, 3.6, 3.7, and 4.5. If you have the
panel-mount version, DTM-151-PS, mounting instructions are to be found in section 3.11. For help regarding
operation in electrically noisy areas, see section 3.12.
3.2 CONNECTING THE HALL PROBE
Before handling the probe, please read the following:
Group3 Hall probes are built to be as robust as possible for a small, precision device. However, it is most
important that certain precautions be taken when handling and installing probes so that they are not damaged
or destroyed, and to preserve their accurate calibration.
Mount the probe head so there is no pressure which will tend to bend or depress its ceramic rear surface. If
the probe head is clamped, make sure the surface in contact with the ceramic is flat and covers the whole of
the ceramic surface. Do not apply more force than is required to hold the probe in place. Any strain on the
ceramic will alter the probe's calibration, and excessive force will destroy the Hall element inside.
When the probe head is mounted, the cable should be clamped firmly nearby so it
cannot be torn away from the probe head if accidentally pulled. The flexible section adjacent to the probe head
can be carefully folded to allow the cable to come away in any direction but avoid repeated flexing of this
section.
Keep the cable out of the way of foot traffic. Do not pinch the cable or drop sharp or heavy objects on it. A
severed cable cannot be re-joined without altering the probe's performance and requires factory repair and re-
calibration.
Your DTM must be used with a Group3 Hall probe. The probe may be one supplied with your teslameter, or it
may have been obtained separately. In any case, calibration is preserved when probes are exchanged between
instruments. In order to obtain specified performance, the DTM-151 should be used only with a -141 and -231
series probes.
DTM-151 (serial) User’s Manual 3-1

The standard probe cable length is 2 meters. Probes with non-standard cable lengths up to 30 meters may be
ordered from your Group3 supplier. The cable used for Group3 probes is shielded to reduce pickup of induced
noise from external sources. Such noise may reduce the accuracy of the instrument, cause malfunctioning, or
in extreme circumstances even result in damage to the internal circuitry. See section 3.12.
With the DTM unpowered, plug the probe connector into the instrument. The pin side of the plug is inserted
into the large opening in the rear of the DTM, with the plug's label uppermost when the instrument is standing
right way up. It is easy to find the correct mating position for the plug, and then push it fully home, but if any
difficulty is experienced at first, remove the DTM's top cover by loosening the central screw and lifting the
cover off. Now it is possible to see when the plug is centrally located and its overhang slides over the card-
edge receptacle, ensuring that its pins engage correctly. Tighten the connector retaining screws finger tight.
Do not leave these screws loose as they form part of the shielding system around the teslameter. The
teslameter should always be used with both covers attached.
Always disconnect power from the teslameter before connecting or disconnecting the probe. If the probe
connector is inserted or withdrawn with power on, data stored in memory may be corrupted, leading to
erroneous field readings. If this happens, the defaults switch S2-8 should be switched ON then OFF while power
is applied. See Fig. 5 and Table 4.
When no probe is connected to the DTM, the display reads noProbE.
3.3 CONNECTING THE POWER SOURCE
All teslameter versions, except for the L option, are supplied with a plug-pack. Connect the plug-pack to a
convenient ac power source, first checking the voltage marked on the plug-pack and insert the cable connector
into the power receptacle on the DTM rear panel.
Instead of the plug-pack, the unit can be powered by any convenient source of ac or dc (either polarity), 9 to
15 volts, capable of supplying 0.7A rms ac or 0.5A dc. The cable connector required for power connection to
the DTM is a standard coaxial plugpack connector with 2.1mm center hole and is generally available from
electronics suppliers.
For extra immunity to damage and operational disturbance caused by serious high voltage sparking near the
teslameter, the use of the Group3 model PS12D7 off-line switch-mode power supply and the Group3 ferrite kit
part no. 11000036 is recommended. These accessories will greatly reduce the amount of electrical transient
energy entering the teslameter. The ferrite kit includes a suppressor which fits to the probe cable near the
point of entry to the teslameter to reduce the effects of transients picked up on the probe cable. For a full
discussion of techniques to promote trouble free operation in electrically noisy environments, see section 3.12
of this manual.
3-2 DTM-151 (serial) User’s Manual

Powering the L option teslameter -
The L option will accept power input from the ac power line.
Access to the power input terminals of the L option is obtained by taking off the orange cover; remove the 3
fixing screws to release the cover.
Use 3-conductor power cord. For safety from electrical shock it is essential to provide a reliable ground
connection to the DTM case. Make sure the ground wire is connected as shown in Fig. 1. Strip about 60 mm
(2.5 in) of outer jacket from the cord, and strip 5 mm (3/16 inch) of insulation from the 3 wires. Pass the cord
through the grommeted hole in the cover. Loosen the screw securing the cable clamp and pass the cord through
the clamp. Tighten the clamp on the outer jacket. Terminate the wires and fit links according to the supply
voltage as set out in Fig. 1 below. Replace the orange cover, making sure that wires are not pinched in the
process. For safety reasons, do not operate the unit with the cover off.
Note that input power protection is provided by a thermal fuse wound into the power transformer. This fuse
will open in the event of transformer overheating rather than on excess current. The power input must be
connected as shown to include the thermal fuse in the circuit correctly. If a fault causes transformer
overheating and subsequently the fuse opens, the transformer must be replaced with the genuine Group3 part.
Fig. 1. Power Input Connections of the -L option
If desired, the wiring may be protected by installing an external fuse in the ac power feed. Suggested fuse
ratings are 200 mA for 115 volts, or 100 mA for 208 and 230volt operation.
When the unit is first powered up, the display shows Group3 for 2 seconds before field measurements appear.
If the Hall probe is not plugged in, the field reading display is replaced with noProbE.
DTM-151 (serial) User’s Manual 3-3

3.4 FIBER OPTIC CONNECTIONS
The DTM-151-_S has facilities for communicating with external devices, such as computers or terminals, using
its serial I/O ports. The teslameter may also be set up to relay communications through other compatible Group3
devices, using the Group3 Communication Loop. See section 4.5.
There are 3 bi-directional ports, 2 using standard RS-232C signals, the third employing fiber optics. In
electrically noisy environments, or where ground loops could be troublesome, or if a voltage gradient must be
traversed, it is advisable to use fiber optics for the serial data link. The teslameter's fiber optic ports accept
Hewlett-Packard HFBR-3500 series fiber optic cables up to 60 meters in length.
Fiber optic cables are fitted with a blue connector one end and a grey connector at the other. Although
functionally identical, the colours make it easier to keep track of cable routing when connecting up a system.
The convention is to use grey at send ports and blue at receive ports. To connect the cables, simply push the
connector in through the appropriately labelled hole in the teslameter’s rear panel. The connector will snap into
place. To disconnect, give the cable a gentle tug. Inspect the cable ends to ensure the inner core has not
retracted. Loose cable ends should be protected from dirt and scratching.
3.5 ELECTRICAL SERIAL DATA INPUT/OUTPUT CONNECTIONS
Serial data connections to the teslameter can be made electrically in two ways, as alternatives to the fiber
optic method described in the previous section:
3.5.1 The G3CL Ports
The two 4-way Group3 Communication Loop connectors, one each for send and receive, provide an electrical
alternative to the fiber optic ports, and handle the same data. Signal levels are equivalent to RS-232C
levels. RS-232C handshake signals are not present at these ports.
The G3CL ports allow serial connections to be made using a simple twisted pair or coaxial cable for each data
direction and avoid consideration of handshake signals if these are not required in the application.
Connection to the G3CL ports requires two Molex receptacles type M5051-4 with M2759 crimp terminals. Pin
assignments are given in Table 1 below. The RS-232C standard allows cable lengths of up to 50 ft, but in
practice longer cables will work reliably, particularly at the lower bit rates. Connection is made through the
labelled opening in the teslameter's rear panel.
3-4 DTM-151 (serial) User’s Manual

In the device at the send port, pin 2 (common) is connected to circuit common. However, at the receive port
the signal drives an optical coupler without any direct connection to the circuitry. This arrangement avoids
ground loops which can inject noise into the link and give rise to transmission errors.
pin use
1 signal active
2 signal common
3 cable shield (optional)
4 not used
Table 1. G3CL Connector Pin Assignments
3.5.2 The RS-232C Connector
The RS-232C connector is a 26-pin field which can be used to connect the teslameter to a computer, terminal,
printer, or other external equipment which can send and receive RS-232C signals. The pin field will connect
with a standard 26-way flat cable socket connector, for example 3M type 3399-6000. The pin assignments
follow those of the standard 25-way RS-232C connector, starting at pin 1 and omitting pin 26. If desired, an
adaptor cable may be used to allow cables with 25D connectors to be plugged in to the teslameter.
In order to avoid the conflicts and confusion which often arise when RS-232C is used to interconnect equipment
which cannot be classified strictly as either communications or terminal equipment, the DTM has been provided
with a number of user options in the form of moveable jumpers and wire-wrap posts on the Processor Board.
Thus pins 2 and 3 may be connected to send and receive signals, respectively, or vice versa.
Similarly, a number of the most-used RS-232C handshake signals are provided on the board, and these may be
routed to appropriate pins on the connector if desired. But their use is optional. In most cases no active
handshaking need be used. Some external equipment may require certain signal lines to be held high for correct
operation. These options are provided for (see below).
DTM-151 (serial) User’s Manual 3-5

Fig. 2. RS-232C Connector and Jumper Locations
The DTM can provide one output handshake signal, RTS, which is asserted high when the unit has data it
wishes to transmit.
The DTM can also accept up to two input handshake signals, CTS and DCD. If CTS is held low by the external
equipment, then no data will be transmitted. When low, DCD inhibits and initializes the receive input of the
teslameter. DCD must be high to allow the unit to accept incoming data. If these inputs are not connected to
the RS-232C pin field, the relevant pins must be tied to +5 volts on the Processor Board, using the jumpers
provided.
The handshake signals can be used only when the teslameter is connected directly through its RS-232C
connector to an RS-232C compatible device. When several Group3 devices are arranged in a loop using the
Group3 Communication Loop ports, RS-232C handshaking cannot be used. CTS and DCD must be tied high in
this case.
Table 2 below gives the pin assignments and signal names when the teslameter is configured as a Data Terminal
Equipment (DTE). This will be referred to as terminal mode.
3-6 DTM-151 (serial) User’s Manual

The unit can also be set up to behave like a Data Communications Equipment (DCE), for example a modem. The
instrument is then said to be in modem mode. See the RS-232C connector pin assignments for modem mode
below in Table 3. Fig. 2 shows the location of the RS-232C pin field, moveable jumpers and wire-wrap posts
on the Processor Board.
For terminal mode, the send and receive (T/M) jumpers should be pushed onto the square posts lined up parallel
with the long side of the circuit board. In modem mode, the jumpers are set at right-angles to the above.
See Fig. 3.
DTM-151 (serial) User’s Manual 3-7

The option 1 and 2 jumpers configure the relationship between the RS-232C connector and the G3CL ports.
For single device systems, option 2 should be selected. Refer to Fig. 4 below. Section 4.5 describes the use
of the option jumpers in setting up the alternative G3CL arrangements.
22
Fig. 2 also indicates the positions of the wire-wrap posts on which appear the RTS, CTS, and DCD signals, +5
volts and ground, and posts which connect to RS-232C connector pins 4, 5, 6, 8, and 20. These pins may be
wire-wrapped according to the options set out in Tables 2 and 3. When pins are adjacent they may be
connected more easily with push-on jumpers.
3-8 DTM-151 (serial) User’s Manual