Power Measurement 3710 ACM User manual

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Danger
During normal operation of this device, hazardous voltages are present which can
cause severe injury or death. These voltages are present on the terminal strips of the
device and throughout the connected potential transformer (PT), current transformer
(CT), status input, relay, and control power circuits. Installation and servicing should
be performed only by qualified, properly trained personnel. See the 3710 ACM
Installation and Operation Manual for further details.
Warning
This equipment generates, uses, and can radiate radio frequency energy and if not
installed and used in accordance with the 3710 ACM Installation and Operation Manual,
may cause interference to radio communications. It has been tested and found to
comply with the limits for a Class A computing device pursuant to Part 15 of FCC
Rules, which are designed to provide reasonable protection against such interference
when operated in a commercial environment. Operation of this equipment in a
residential area may cause interference in which case the operator will be required to
take whatever measures may be required to correct the interference.
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3710 ACM is a trademark of Power Measurement Ltd. DF1 is a trademark of Allen-
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© 1998 Power Measurement Ltd.
The information contained in this document is believed to be accurate
at the time of publication, however, Power Measurement Ltd. assumes
no responsibility for any errors which may appear here and reserves
the right to make changes without notice.
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For further information or technical assistance,
please contact your local Power Measurement
representative, or Customer Service at one of
the following locations:

Jim M. Bilach
Systems Engineer
Ver. 1.0 : December 19, 1989
Ver. 2.0 : March 08, 1990
Ver. 3.0 : November 26, 1990

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TABLE OF CONTENTS
SECTION TOPIC PAGE
1 INTRODUCTION
1.1 - Purpose of the Communications Protocol 5
1.2 - Communications Protocol Revisions 6
2 DETAILED DESCRIPTION OF THE COMMUNICATIONS PROTOCOL 7
2.1 - Protocol Ground Rules 7
2.2 - Hardware Configuration 8
2.3 - Description of the Packet Structure 9
2.4 - Broadcast Packets 14
2.5 - Network Timing Considerations 14
2.6 - 3710 ACM Timing Considerations 15
3 PACKET COMMUNICATIONS WITH THE MODEL 3710 ACM 16
3.1 - 3710 ACM Set-up Packets 17
3.2 - 3710 ACM Data Packets 34
3.3 - 3710 ACM Log Packets 47
3.4 - 3710 ACM Control Packets 64
4 LIST OF THE 3710 ACM PACKET COMMAND TYPES 72

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1.0 - INTRODUCTION
This document details the serial communications protocol used to pass
commands, information and data between the model 3710 ACM Power Meter
and the Allen-Bradley line of programmable logic controllers (PLC) and
communication interface products.
This document provides the information necessary for a 3rd party OEM to
develop in-house software to communicate with the model 3710 ACM Power
Meter.
Additional information concerning 3710 ACM Power Meter operations is
found in the 3710 ACM Installation and Operation Manual. Information
concerning Allen-Bradley communication protocol is found in the Allen-
Bradley Data Highway/Data Highway Plus Protocol and Command Set
Reference Manual.
The information contained in this document is confidential and is
released to the reader on the understanding that it will not be copied
or distributed in any way, to any other party.
1.1 - PURPOSE OF THE COMMUNICATIONS PROTOCOL
The purpose of the communications protocol is to allow information and
data to be efficiently transferred between an Allen-Bradley PLC and a
3710 ACM Power Meter. This includes:
1) Allowing configuration and interrogation of all 3710 ACM Power
Meter set-up parameters from the Allen-Bradley PLC.
2) Allowing interrogation of all data measured by a 3710 ACM Power
Meter.
3) Allowing the configuration and interrogation of all 3710 ACM
setpoint parameters.
4) Allowing the control of the 3710 ACM relays.
5) Allowing interrogation of the 3710 ACM event and min/max logs.

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1.2 - COMMUNICATIONS PROTOCOL REVISIONS
This section details the changes made to each new version of the Serial
Communications Protocol Document.
Ver. 1.0 - Initial draft of the Serial Communications Protocol Document
(Released 89/12/19).
Ver. 2.0 - Corrected delta mode line-to-line average voltage from
incorrect line-to-neutral average voltage readings in Short
Real-Time Data Packet.
Ver. 3.0 - Major Revision: Upgraded protocol to support RS-485 serial
communications.

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2.0 - DETAILED DESCRIPTION OF THE COMMUNICATIONS PROTOCOL
2.1 - PROTOCOL GROUND RULES
The following rules define the protocol for information transfer between
the Allen-Bradley PLC / Communication Interface Products and the 3710
ACM Power Meter on the RS-485 serial communications loop.
The 3710 ACM uses the Allen-Bradley PLC-2 protocol in order that it may
communicate with Allen-Bradley line of PLCs and Communication Interface
Products.
1) All communications on the RS-485 loop conforms to a MASTER/SLAVE
scheme. In this scheme, information and data is transferred between a
single MASTER Allen-Bradley PLC and up to 32 SLAVE 3710 ACM Power
Meters.
2) The Allen-Bradley PLC will initiate and control all information
transfer on the RS-485 communications loop.
3) Under no circumstances will a SLAVE 3710 ACM Power Meter initiate a
communications sequence.
4) All communication activity on the RS-485 loop occurs in the form of
"PACKETS", a packet being simply a serial string of data bytes. The
maximum number of bytes contained within one packet is 255. The bytes
that comprise a packet consist of standard asynchronous serial data
transmitted with 8-bits per data byte, no parity and one stop bit.
5) This protocol uses a command / reply message packet format in which
the Allen-Bradley PLC transmits a command type packet to the 3710 ACM
Power Meter and the 3710 ACM answers the PLC with a reply type packet.
This protocol uses two of the Allen-Bradley Message Packet Formats from
the PLC-2 or Basic Command Set: Unprotected Read and Unprotected Write.
6) The 3710 ACM Power Meters on the RS-485 communications loop assume
the role of the "loop foreman" when data is requested by the PLC. The
"loop foreman" is responsible for all acknowledgements back to the PLC
for itself and 3710 ACMs that are non-existent or do not respond. This
eliminates the 30 second timeout from the Allen-Bradley Communications
Module which inhibits communications.
7) In the case where the 3710 ACM Power Meters receive a packet that
contains an unknown message type address, the "loop foreman" will
respond with its last packet except the STS (Status) byte of the packet
will contain a 10 Hex. The 10 Hex in the Allen-Bradley protocol
indicates an "illegal command" error.
8) In the case where the 3710 ACM Power Meters receive a packet that
contains an unknown unit id address, the "loop foreman" will respond
with its last packet except the STS (Status) byte of the packet will

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contain a 30 Hex. The 30 Hex in the Allen-Bradley protocol indicate a
"remote host missing" error.
2.2 - HARDWARE CONFIGURATION
The following section describes the hardware configuration required to
connect a single 3710 ACM Power Meter or up to 32 3710 ACM Power Meters
to a single Allen-Bradley PLC through several different Allen-Bradley
Communications Interface Modules.
In order for 3710 ACMs to communicate with an Allen-Bradley PLC through
the Allen-Bradley Data Highway, it must do so with the aid of the Allen-
Bradley Communication Interface Modules. The two modules that the 3710
ACM will communicate with are the 1770-KF2 Series B Communication
Interface Module and the 1785-KE Data Highway Plus RS-232C
Communications Interface Module.
The Allen-Bradley Communication Interfaces must be configured using the
following settings: full duplex, BCC error checking, no parity, no
embedded responses, yes to detect and ignore duplicate messages and no
to using handshaking signals.
In order for multiple 3710 ACMs (using the RS-485 serial communications
standard) to communicate with a Allen-Bradley Communications Interface
Module (using the RS-232C serial communications standard), a device
called a COM32 convertor must be used in the system. The COM32 is an
RS-232C to RS-485 serial communications convertor which allows the
translation of the serial data stream from one standard to another.
A single 3710 ACM may be directly connected to an Allen-Bradley
Communications Interface Module using the RS-232C standard.
The Allen-Bradley PLC-5/15 may be connected directly to the Data Highway
without the use of the communication interfaces.

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2.3 - DESCRIPTION OF THE PACKET STRUCTURE
The following section describes the structure of the packet used to
transfer data and information between the Allen-Bradley PLC and the 3710
ACM Power Meter. The packet structure will be broken down into
appropriate fields and the equipment relevant to each field will be
mentioned.
Every packet is composed of six fields:
1) The Message Frame Establishment Field
2) The Interface Address Information Field
3) The Control Information Field
4) The Data Field
5) The Message Frame Termination Field
6) The Error Detection Field
2.3.1 - MESSAGE FRAME ESTABLISHMENT FIELD
The Message Frame Establishment field is used to determine the start of
a packet (start of frame delimiter). This field is fixed in length and
contains two sub-fields, the Data Link Escape (DLE) SUB-FIELD and the
Start of Text (STX) SUB-FIELD. These two bytes are used by the Data
Link Layer of the Allen-Bradley Communication Interface and the 3710 ACM
Power Meter only.
THE DATA LINK ESCAPE (DLE) SUB-FIELD (1 Byte)
This sub-field contains a single byte control character used to
indicate the start of a message packet.
THE START OF TEXT (STX) SUB-FIELD (1 Byte)
This sub-field contains a single byte symbol character used to
indicate the start of a message packet.
2.3.2 - INTERFACE ADDRESS INFORMATION FIELD
The Interface Address Information field is fixed in length and contains
two sub-fields, the DESTINATION ADDRESS (DST) SUB-FIELD and the SOURCE
ADDRESS (SRC) SUB-FIELD. These two bytes are used by the Network Layer
of Allen-Bradley Communication Interface and the 3710 ACM Power Meter
only.
THE DESTINATION ADDRESS (DST) SUB-FIELD (1 Byte)
This byte contains the address of the device (PLC or Communication
Interface connected to the 3710 ACM) that the packet is being sent
to.

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THE SOURCE ADDRESS (SRC) SUB-FIELD (1 Byte)
This byte contains the address of the device (PLC or Communication
Interface connected to the 3710 ACM) from which the packet
originated.

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2.3.3 - CONTROL INFORMATION FIELD
The Control Information field is fixed in length and contains three sub-
fields, the COMMAND TYPE SUB-FIELD (CMD), the STATUS SUB-FIELD (STS) and
the TRANSACTION IDENTIFIER SUB-FIELD (TNS). These four bytes are used
by the Allen-Bradley PLC, Allen-Bradley Communication Interface and the
3710 ACM Power Meter.
THE COMMAND TYPE SUB-FIELD (1 Byte)
This byte is used to define the activity to be performed by the
command at the destination station. The following lists describes
the Allen-Bradley command type values that are used in this protocol:
CMD DESCRIPTION OF CMD
01 Unprotected Read Command
41 Unprotected Read Reply
08 Unprotected Write Command
48 Unprotected Write Reply
An Unprotected Read obtains data from the 3710 ACM while an
Unprotected Write delivers data to the 3710 ACM. The commands are
only sent from the PLC and the replies are only sent from the 3710
ACM.
THE STATUS SUB-FIELD (1 Byte)
This byte indicates the status of the message transmission. A status
byte value of 00 indicates a successful transmission. Errors such as
10 Hex (illegal command) or 30 Hex (remote host missing) will be
indicated in this location.
THE TRANSACTION IDENTIFIER SUB-FIELD (2 Bytes)
These two bytes contain a unique 16-bit transaction identifier. The
purpose of this field is to associate the replying packet with the
one that initiated the command. In other words, a commanding station
can identify its’ reply packet.

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2.3.4 - DATA FIELD (0 up to 244 Bytes)
The Data field will vary in length according to the type of command
(CMD) contained within the packet. The following will describe the
structure of the data and the order that they are sent in the packet.
Secondly, the data structure fields for each command used will be
described. These bytes are used by the Application Layer of the Allen-
Bradley PLC and the 3710 ACM Power Meter.
Packet Data Structure
In general, most data values sent to and from a model 3710 ACM consist
of a 4 byte value. Each 4 byte value can be treated as two WORDS, a LOW
ORDER WORD and a HIGH ORDER WORD. In a similar manner, each word is
composed of a two byte value, one being a LOW ORDER BYTE and the other
being a HIGH ORDER BYTE.
The order of the 4 bytes that represent any single parameter is
important. The rules that specify this order are as follows:
ALL PARAMETERS THAT REQUIRE TWO WORDS ARE SENT TO THE ACM IN THE
ORDER LOW WORD FIRST, HIGH WORD SECOND.
ALL WORDS ARE COMPOSED OF TWO BYTES AND ARE SENT TO THE ACM IN
THE ORDER LOW BYTE FIRST, HIGH BYTE SECOND.
EXAMPLE: A 3710 ACM parameter has the value 12345678 Hex.
This 4 byte value can be split into two WORDS,
LOW ORDER WORD = 5678 Hex.
HIGH ORDER WORD = 1234 Hex.
The LOW ORDER WORD can be split into two bytes,
LOW ORDER BYTE = 78 Hex.
HIGH ORDER BYTE = 56 Hex.
The HIGH ORDER WORD can be split into two bytes,
LOW ORDER BYTE = 34 Hex.
HIGH ORDER BYTE = 12 Hex.
This 4 byte parameter would be transmitted LOW ORDER WORD FIRST, LOW
ORDER BYTE FIRST, hence the 4 bytes that comprise this value would be
transmitted in the order 78 56 34 12.
Read command response packets issued by the 3710 ACM have the following
common elements at the start of the a field.
Device Type: integer representation of 3710 (or 0E7E Hex).
Software Revision: 16 bit value, with each 4 bit nibble representing a
digit in the version number X.X.X.X (ie. revision
2.1.0.0 would be represented by 2100 Hex).
Unit ID: 8 bit even value representing the transmitting 3710
ACM unit address or ID.
Input Mode: 0 = 4 Wire WYE.
1 = 3 Wire DELTA.
2 = 3 Wire, Single Phase
3 = Demonstration

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COMMAND DATA FIELD FORMATS
The data field format for command and reply message packets of Allen-
Bradley Unprotected Read and Write commands are as follows. These two
message formats can be found in the basic command set of the Allen-
Bradley Data Highway/Data Highway Plus Protocol and Command Set
Reference Manual.
Unprotected Read Command Format
This data field contains an ADDRESS SUB-FIELD (ADDR) and a SIZE SUB-
FIELD (SIZE). The ADDR is a two byte field which is broken down into
two separate bytes. The high order byte contains the location or type
of data in the 3710 ACM. The low order byte contain the even valued
3710 ACM unit address or unit id in which the PLC can uniquely identify
the meter. These two bytes form the Message Type Address found later in
this document. The PLC cannot request data at any address except those
defined as Message Type Addresses. The following section entitled
Destination Table Address Conversion describes how one converts the
hexadecimal Message Type Address into the octal Destination Table
Address which is required by the Allen-Bradley PLC-5 ladder logic
program communication instruction called the Message Block. The SIZE is
a one byte field which specifies the number of bytes to be transferred
by the packet. The SIZE value is "fixed".
Unprotected Read Reply Format
This data field contains the data reply to the read command in the form
of a DATA SUB-FIELD (DATA). In this field, up to 244 bytes of data are
transferred from the 3710 ACM.
Unprotected Write Command Format
This data field contains an ADDRESS SUB-FIELD (ADDR) and a DATA SUB-
FIELD (DATA). The ADDR is a two byte field which contains the protocol
defined message type address as in the preceding Unprotected Read
Command Format section. The DATA field may transfer up to 242 bytes of
data to the 3710 ACM.
Unprotected Write Reply Format
This reply packet contains no data field.
DESTINATION TABLE ADDRESS CONVERSION
In order to communicate with a 3710 ACM from a PLC-5, the Message Type
Address (which contains the type of data and the unit id of the 3710
ACM) must be converted to a value which can be directly entered into the
PLC-5 Message communication instruction Destination Table Address. The
following will describe this:
First, take the higher order Message Type Address (ADDR) hexadecimal
byte value and append it with the lower order Message Type Address
hexadecimal byte value. Divide this hexadecimal word value by two and
then convert this hexadecimal value to a octal (base 8) value. The

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result is the desired Destination Table Address. The following example
will clarify the procedure:
The request is for the Long Real-Time Data Packet (High Order Message
Type Address: 04 hexadecimal) from 3710 unit id number 156 (Low Order
Message Type Address: 156 decimal = 9C hexadecimal).
First, append the low order byte to the high order byte in hexadecimal:
Message Type Address = 049C Hex.
Second, divide the above word by two in hexadecimal:
Message Type Address = 024E Hex.
Third, convert the previous result from hexadecimal base to octal base
to yield the PLC-5 Message Instruction Destination Table Address:
Destination Table Address = 1116 Octal.
2.3.5 - MESSAGE FRAME TERMINATION FIELD
The Message Frame Termination field is used to detect the end of a
packet (end of frame delimiter). This field is fixed in length and
contains two sub-fields, the Data Link Escape (DLE) SUB-FIELD and the
End of Text (ETX) SUB-FIELD. These two bytes are used by the Data Link
Layer of Allen-Bradley Communication Interface and the 3710 ACM Power
Meter only.
THE DATA LINK ESCAPE (DLE) SUB-FIELD (1 Byte)
This sub-field contains a single byte control character used to
indicate the end of a message packet.
THE END OF TEXT (ETX) SUB-FIELD (1 Byte)
This sub-field contains a single byte symbol character used to
indicate the end of a message packet.
2.3.6 - ERROR DETECTION FIELD (1 Byte)
The Error Detection Field contains only 1 byte. This byte is an eight
bit error code used to detect packets that have been corrupted during
transmission. This eight bit code is the last byte transmitted in the
packet. This byte is used by the Data Link Layer of Allen-Bradley
Communication Interface and the 3710 ACM Power Meter only.
The error code is an eight bit Longitudinal Redundancy Check (LRC) which
is complemented prior to transmission.
The LRC is calculated by a simple arithmetic sum over all preceding
message bytes contained within the packet with the exception of the
start of packet frame delimiter bytes (DLE and STX) and the end of
packet frame delimiter bytes (DLE and ETX). The complemented LRC byte

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is equivalent to the Block Check Character (BCC) used by Allen-Bradley
Communication Products.
2.4 - BROADCAST PACKETS
Provisions have been made for the use of broadcast commands within the
RS-485 data transfer protocol. The purpose of this is to allow all
Slave devices to receive the same command from the Master station. This
feature is very useful in situations such as time synchronization of
slave clocks.
When broadcast packets are transmitted by the PLC, all Slave devices
will receive and perform the packet command but the device that has been
set as the "loop foreman" will send a response packet. This is to avoid
the possibility of having more than one Slave Device response at one
time. Communications from the Master PLC to the Slave devices must not
begin with a broadcast packet because no device has had the chance to
setup itself as a "loop foreman". Therefore, communicate with a single
meter on the RS-485 loop before transmitting any broadcast packets.
2.5 - NETWORK TIMING CONSIDERATIONS
Network timing considerations for the transfer of packets between units
on the RS-485 loop must conform to the following rules.
1) The time between the end of a PLC message request packet and the
beginning of a SLAVE STATION message response packet must not be
less than 5 milliseconds.
T response min = 5 milliseconds
This is to provide the PLC with enough time to prepare for the
reception of the message response packet from the SLAVE STATION.
2) The time between the end of a PLC message request packet and the
beginning of a SLAVE STATION message response packet must not
exceed 500 milliseconds.
T response max = 500 milliseconds
3) The minimum time between the end of any PLC message packet and the
beginning of the next PLC packet is device dependent.
T PLC min = [device dependent]
4) The minimum time between the end of a SLAVE STATION response packet
and the beginning of the next PLC message packet is device
dependent.
T slave min = [device dependent]
5) The maximum time between any two data bytes within a packet must
not exceed 50 milliseconds.
T byte max = 50 milliseconds

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2.6 - 3710 ACM TIMING CONSIDERATIONS
1) The 3710 ACM requires a 100 millisecond dead space between the end
of any response packet on the RS-485 loop and the start of a new command
packet sent by the Master PLC.
2) Sequential transmissions from the Master PLC to the 3710 ACM meters
must be 100 milliseconds apart (ie: 100 millisecond dead space).
3) Any 3710 ACM that receives a valid command packet from the Master
PLC will begin sending its response packet within 100 milliseconds (10
milliseconds typically).

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3.0 - PACKET COMMUNICATIONS WITH THE MODEL 3710 ACM
This section details all packet communications into and out of the model
3710 ACM Power Meter. Command packets sent to the 3710 ACM from the
Allen-Bradley PLC and reply packets sent from the PLC to the 3710 ACM
are divided into three categories according to their function:
1) The packets listed in the first category are used to configure and
set-up the 3710 ACM Power Meter prior to operation.
2) The packets listed in the second category are used to extract the
data measured by the model 3710 ACM.
3) The packets listed in the third category are used to perform 3710
ACM control functions.