ROOTECH ACCURA 3500 Communication User Guide

Brand: ROOTECH

Model: ACCURA 3500

Type: Communication User Guide

High Accuracy Digital Power Meter

Added with Extension modules

Suits your various applications

Communication Guide[English]

Rev 1.3

Page 2

Notice

Limitation of Liability

Rootech Inc. reserves the right to make changes in the device specifications shown in

this User’s Guide without notice. Rootech Inc. advises customers to obtain the latest

specifications of device before giving orders to confirm that the information being relied

on by the customer is up to date.

In the absence of written agreement to the contrary, Rootech Inc. assumes no liability

for Rootech Inc. applications assistance, customer’s system design, or infringement of

patents or copyrights of third parties by or arising from the use of devices described

herein.

Except to the extent prohibited by applicable law, under no circumstances shall

Rootech Inc. be liable for consequential damages sustained in connection with said

product and Rootech Inc. neither assumes nor authorizes any representative or other

person any obligation or liability other than such as is expressly set forth herein.

The information contained in this document is believed to be accurate at the time of

publication, however, Rootech Inc. assumes no responsibility for any errors which may

appear here and reserves the right to make changes without notice.

Page 3

Standard Compliance

CE Approved

EN61326 and IEC61010

35DX

MEASURING EQUIPMENT

E258934

KSA 9001:2001/ ISO 9001:2001

QMS-1347

Page 4

Warranty Information

For products and software that are sold or licensed by Rootech Inc. during the period

from the date of receipt by you until the present, Rootech warrants only to the original

purchaser.

The purchased products other than software shall be substantially free from material

defects in material and workmanship by Rootech for two years from the date receipt by

you.

The software itself is provided “as is” without any warranty of any kind.

Limitation of Warranty

These limited Warranties shall not apply to any product that has been subject to

alteration, accident, misuse, abuse, neglect or failure to exactly follow Power

Measurement's instructions for operation and maintenance.

In order for the original purchaser to make a claim under the warranties described

above, the original purchaser must promptly contact Rootech headquarter. After

receiving such notice, Rootech may either in Rootech’s sole discretion, examine the

product at the original purchaser’s site or issue shipping instructions to the original

purchaser to return the relevant product to Rootech for examination at the original

purchaser’s expense, transportation charges prepaid.

If after examining the product Rootech reasonably confirms that such examined

product does not meet the warranties, then the original purchaser’s sole remedy and

Rootech’s sole obligation or liability shall be, at Rootech’s option, to repair, replace or

refund the price paid for that product.

Regardless of whether any remedy set forth herein fails of its essential purpose, except to

the extent the following limitation is prohibited by applicable law, Rootech shall not, in

any event or under any legal claim or theory, be liable to the original purchaser or any

other person or entity for special, indirect, incidental, punitive, liquidated, special or

consequential damages whatsoever with respect to any purchased product, including,

without limitation, business interruption, loss of use, profit or revenue, even if Rootech has

Page 5

been advised of the possibility of such damages. To the extent that a limitation or

exclusion of consequential damages are prohibited by applicable law, then Rootech’s

liability shall be limited to twice the amount of the relevant purchased product.

Rootech shall not be liable for any claim- other than a claim solely for the breach of one

of the above warranties that is made in accordance with the above described

procedures- made by the original purchaser, its employees, agents, or contractors for

any loss, damage, or expense incurred due to, caused by, or related to any purchased

product

Any technical assistance provided by Rootech's personnel or representatives in system

design shall be deemed to be a proposal and not a recommendation. The responsibility

for determining the feasibility of such proposals rests with the original purchaser and

should be tested by the original purchaser.

It is the original purchaser’s responsibility to determine the suitability of any product and

associated documentation for its purposes. The original purchaser acknowledges that

100% "up" time is not realizable because of possible hardware or software defects. The

original purchaser recognizes that such defects and failures may cause inaccuracies or

malfunctions.

Only the terms expressed in these limited Warranties shall apply and no distributor,

corporation or other entity, individual or employee of Rootech or any other entity is

authorized to amend, modify or extend the Warranties in any way.

Page 6

Revision History

The following versions of the Accura 3500 Communication Guide have been released.

Revision #

Revision date

Description

Firmware version

Revision 1.0

2006. 06. 30

Initial release

Revision 1.1

2007. 04. 24

Added Short-formed data block

1.18

Added a register of extension

module configuration.

1.22

Revision 1.2

2007. 07. 13

Figure and comm examples

modified

Revision 1.3

2024. 01. 12

Added Energy of Quadrant 4

Corrected typos in the main text

and bookmark

 
 
 
Page  7 
Contents 
 
 
Chapter 1 Serial Communication .................................................................................................................... 9 
Overview ........................................................................................................................................................................................... 9 
Master/Slave Multi-drop ................................................................................................................................................. 9 
Modbus RTU Protocol ..................................................................................................................................................... 9 
Communication ........................................................................................................................................................................... 10 
RS485 Communication Timing .................................................................................................................................. 11 
Packet Recognition Time .............................................................................................................................................. 11 
Holding Time before transmitting Request Packet ......................................................................................... 11 
Chapter 2 Communication Setup ................................................................................................................. 12 
Communication Wiring ............................................................................................................................................................ 12 
Setup ................................................................................................................................................................................................. 13 
Setup Mode ........................................................................................................................................................................ 13 
Chapter 3    Modbus RTU Protocol ............................................................................................................... 16 
Packet Field of Modbus RTU ................................................................................................................................................ 16 
Slave Address Field ......................................................................................................................................................... 16 
Function Field..................................................................................................................................................................... 16 
Data Field ............................................................................................................................................................................. 16 
Error Check Field .............................................................................................................................................................. 17 
Exception Responses ...................................................................................................................................................... 17 
Broadcast Packets............................................................................................................................................................. 18 
Packet Communications .......................................................................................................................................................... 19 
Function 03: Read Holding Registers ..................................................................................................................... 19 
Function 06: Write Single Register to Meter ...................................................................................................... 20 
Function 16: Write Multiple Registers to Meter ............................................................................................... 20 
Reserved Registers........................................................................................................................................................... 21 
Invalid Registers ................................................................................................................................................................ 21 
Chapter 4    Modbus RTU Map ...................................................................................................................... 22 
Overview ......................................................................................................................................................................................... 22 
System information section ................................................................................................................................................... 24 
Configuration section ............................................................................................................................................................... 25 
Measurement section ............................................................................................................................................................... 27 
THD, k Factor section ................................................................................................................................................................ 29 

 
 
 
Page  8 
Extra energy section .................................................................................................................................................................. 29 
Demand, Maximum, Minimum section ........................................................................................................................... 30 
Harmonic section ........................................................................................................................................................................ 33 
Vector diagram section† .......................................................................................................................................................... 34 
Waveform section....................................................................................................................................................................... 35 
Demand trend section ............................................................................................................................................................. 37 
Reset section ................................................................................................................................................................................. 37 
DIO module section† ................................................................................................................................................................. 38 
DI module section† .................................................................................................................................................................... 39 
DO module section† .................................................................................................................................................................. 40 
AI module section† ..................................................................................................................................................................... 41 
AO module section† .................................................................................................................................................................. 41 
Short-formed data block Section ....................................................................................................................................... 42 
Data formats ................................................................................................................................................................................. 46 
Parameter Calculation .............................................................................................................................................................. 48 
Fixed scale ........................................................................................................................................................................... 48 
Variable scale ...................................................................................................................................................................... 48 
APPENDIX A    CRC-16 Calculation ................................................................................................................ 50 
CRC-16 Generation .................................................................................................................................................................... 50 
CRC Generation Procedure.......................................................................................................................................... 50 
CRC table ............................................................................................................................................................................. 51 
APPENDIX B    Modbus RTU C Code Example ............................................................................................ 52 
Data Receiving and CRC Generation& Checking ....................................................................................................... 52 
Request Packet Generation ......................................................................................................................................... 52 
Response Packet Checking .......................................................................................................................................... 52 
CRC functions ..................................................................................................................................................................... 53 
 
 
 

Page 9

Chapter 1 Serial Communication

Overview

Accura 3500 has a RS485 port on the rear side of meter for Master/Slave communication

in the field, and supports Modbus RTU protocol.

Modbus RTU protocol is a industry standard to efficiently transfer information of

measuring and control between master[PC or PLC] and slave[local devices, Accura

3300/3500/3550/7500].

Master/Slave Multi-drop

◼ All communications on network conforms to a Master/Slave scheme.

◼ Master will initiate and control all information on the communications loop.

◼ Under no circumstances A Slave device initiate a communications sequence.

◼ All communications occurs in the form of Packet, a packet being simply a serial

string of 8-bit bytes.

◼ All Packets transmitted by the Master are requests. All Packets transmitted by a

Slave are responses.

◼ At most one Slave can respond to a single request from a Master.

Modbus RTU Protocol

◼ Industry standard protocol for general users.

◼ Modbus RTU is recommended.

◼ Designed according to Modicon Modbus RTU specifications.

◼ Provides selective data communications by address map.

◼ Most of automation programs provides the driver for Modbus RTU.

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Communication

The default serial communication setup of Accura 3500 is 8 data bits, even parity, 1 stop

bit.

The RS485 communications allows multiple devices to be connected on the same bus.

Up to 32 devices can be connected on a single RS485 bus, which consists of a shielded

twisted pair cable more than AWG 22[0.33mm2]. The overall length of the RS485 cable

connecting all devices cannot exceed 1.2km[ or 4000ft].

RS485 Multi-drop Connection Diagram

Warning

The above T bridge – branched off in the middle of communication line- cannot

guarantee the communication reliability by voltage-drop on the line.

To connect an RS485 communication bus to a computer or other RS232 equipped

device, a RS232 to RS485 converter is required. The communication between computer

and Accura 3500 is to connect the Pins, Ta, Tb of the Accura 3500 to the RS485 two lines,

Data+, Data-, and between computer and converter is connected one to one. The

timing flow Between request packet and response packet is followed.

Page 11

RS485 Communication Timing

The figure below shows the timing delay between the Request Packet and the Response

Packet.

Packet Recognition Time

The data packet between master[PC] and slave[devices] has the following format. One

packet consists of consecutive data frames, and frames is recognized as the same

packet for the condition where the distance between frames is within 5ms. At least 10ms

is required to distinguish each packet.

Holding Time before transmitting Request Packet

After receiving the data from meter, at least 10 msec[particularly 13 msec in 57600bps]

is required to send a next request packet.

Page 12

Chapter 2 Communication Setup

Communication Wiring

Pin name

Ta[TRX+], Tb[TRX-]

Connector

Screw terminal[Pluggable]

Wire

1.25 to 3.5 mm2[24 to 14 AWG], Shielded twisted pair

Maximum Cable Length

1219 m[4000 ft]

Maximum Devices/Bus

Note

UL2919 cable is recommended for communication.

Comm Indicator

Comm LED shows green when the meter is transmitting data.

Page 13

Setup

Each of these functions can be accomplished by pressing the Menu, Up, Down, and

Enter buttons on the front panel.

Display mode

View parameter measurements

Setup mode

Configure parameters[wiring, communication, and etc.]

Reset mode

Reset energy, demand, maximum, and minimum.

System mode

View meter system information[meter option, firmware

version].

Module mode

View information of module added on rear side of the meter

Note

SETUP LED shows red when selecting Setup, Reset, System, and Module modes.

Setup Mode

In Setup mode, you can setup menus, such as PT/CT ratio, wiring, and communication

after mounting the meter.

Button Functions in Setup Mode

Button

Function

Enter setup mode by pressing the Up and Down buttons at

the same time.

Move to the previous menu screen.

Move to the next menu screen.

Enter setup edit mode to configure the displayed menu

value.

→ the displayed value blinks†

Exit setup mode and move to display mode.

†It shows that the value of menu item is possible to be changed.

Page 14

Button Functions in Setup Edit Mode

Button

Function

†

Increase the value of menu item.

‡

decrease the value of menu item.

Save the edited value of menu item, and the meter

automatically returns to Setup Mode.

†When pressing at least two seconds, cursor is moved to higher position.

‡When pressing at least two seconds, cursor is moved to lower position.

Note

In setup edit mode, pressing button exits system edit mode and moves to

display mode, without saving the changed value of menu item.

Menu Items

Order

Menu Item

Range

Default

PT ratio

0.1 ~ 999.9

PT ratio =

PT primary/ secondary

1.0

CT ratio

1 ~ 5,000

CT ratio =

CT primary/ secondary

Wiring mode

Single phase 2 wires

Single phase 3 wires

Three phase 3 wires,

Open Delta

Three phase 4 wires

√

Comm address

1 ~ 247

Protocol

Modbus RTU

√

Rootech†

Speed[bps]

1200bps

2400bps

4800bps

9600bps

√

19200bps

38400bps

57600bps‡

Page 15

Parity bits

Even parity

√

Odd parity

None parity

Stop bits

1 ~ 2

†Available only for manufacturer.

‡In 57600bps, after receiving the data from meter, at least 13msecs is required to send a next

request packet. And when writing multiple registers to meter, the size of data word is limited to 24

words.

Page 16

Chapter 3 Modbus RTU Protocol

Accura 3500 supports Modbus RTU.

Packet Field of Modbus RTU

Every modbus packet consists of four fields.

◼ Slave Address Field

◼ Function Field

◼ Data Field

◼ Error Check Field

Slave Address Field

The slave address field of a Modbus packet is one byte in length and uniquely identifies

the slave device involved in the transaction. Valid addresses range between 1 and 247.

A slave device, when receiving a request packet with the slave address field matching

its own address, will perform the command specified in the packet. A response packet

generated by the slave will have the same value in the slave address field.

Function Field

The function field of a Modbus request packet is one byte in length and tells the

addressed slave which function to perform. Similarly, the function field of a response

packet tells the master what function the addressed slave has just performed.

Function[Decimal]

Meaning

Description

Read Multiple register

Obtains the current value from registers

Write Single register

Updates one single register to setup value

Write Multiple registers

Updates more than a register to setup

value

Data Field

The data field of a Modbus request is of variable length, and depends upon the

function. This field contains information required by the slave device to perform the

command specified in a request or data being passed back by the slave device in a

Page 17

response packet. Data in this field is contained in 16-bit or 32-bit registers. Registers are

transmitted in the order of high-order byte first, low-order byte second. This ordering of

bytes is called “Big Endian” format.

Big Endian Example]]

High order byte = 3A hex

Low order byte = 12 hex

This register is transmitted in the order of 12AB

Error Check Field

The checksum field allows the receiving device to determine if a packet has been

corrupted with transmission errors. In Modbus RTU mode, 1 16-bit cyclic redundancy

check[CRC-16] is used. The sending device calculates a 16-bit value using the CRC-16

algorithm. The calculated value is inserted in the error check field.

The receiving device performs the same calculation on the entire packet it receives,

excepting the error check field. If the calculated checksum is not equal to the

checksum stored in the incoming packet, transmission errors occurred and corrupted

the packet. A bad packet will be ignored by the receiving device. Refer to the

“Appendix A CRC-16 Calculation” for details of CRC-16 algorithm.

Packet Format

Slave address

Function

Data

Error check

1 byte

N  2 bytes

2 bytes

Exception Responses

If a Modbus master device sends an invalid command to Accura 3500 or attempts to

read an invalid holding register, an exception response will be generated. The high

order bit of the function code in an exception response is set to 1.

The data field of an exception response contains the exception error code.

Exception Response

Slave address

Function

Exception code

Error check

1 byte

2 bytes

Page 18

Exception code

Name

Description

Illegal Function

Unavailable command in Request Packet

Illegal Address

Unavailable holding address in Request Packet

Illegal Value

Unavailable data transfer in Holding Address

Broadcast Packets

The purpose of a broadcast request packet is to allow all the slave devices to receive

the same command from the master. A broadcast request packet is the same as a

normal request packet, except the slave address field is set to zero.

Page 19

Packet Communications

This section illustrates the Modbus functions supported by the meter.

Function 03: Read Holding Registers

To read meter parameter values, a Master must send the slave device a Read Holding

Registers request packet. The Read Holding Registers request packet specifies a start

Starting Address is a relative address according to register 40000[40001=0, 40002=1,

40101= 100, and etc.]. refer to Appendix B for CRC.

Request

Slave

Function

Starting address

Word count

Error check

1 byte

2 bytes

Example]

A meter is configured as a Modbus slave device with slave address 1. A phase voltage

has the address 40101, and B phase voltage 40102. register 40101 is numbered as 100

when transmitted.

slave address = 1, starting address = 64, word count = 2, crc high = 85, crc low = D4

Slave

Function

Starting Address

Word Count

Error Check

Response

Slave

Function

Byte Count

Data Word 1

---

Data Word N

Error Check

---

1 byte

2 bytes

---

2 bytes

Data word represents the data required in the request packet. Byte count is two times

word count.

Example]

Slave device with address 1 has A phase voltage= 1A1B, B phase voltage= 223B.

slave address = 1, byte count = 4, crc high = D4, crc low = 5F

Page 20

Slave

Function

Byte Count

Data Word 1

Data Word N

Error Check

Function 06: Write Single Register to Meter

To write data to a single register, a master must send the slave device a write single

Request

Slave

Function

Starting Address

Data Word

Error Check

1 byte

2 bytes

Example]

Writes data[78hex] to PT ratio [40053] of the meter with slave address 1.

slave address = 1, starting address = 34, data word = 78, crc high =C8, crc low = 26

Slave

Function

Starting Address

Data Word

Error Check

Response

The response packet to Function 06 command is to send the request packet reversely.

Example]

The response to the request packet is as follows.

Slave

Function

Starting Address

Data Word

Error Check

Function 16: Write Multiple Registers to Meter

To write data to the multiple registers, a Master must send the slave device a Write

Multiple Registers to Meter request packet.

Request

Slave

Function

Starting Address

Word Count

Byte Count

1 byte

2 bytes

1 byte

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ROOTECH ACCURA 3500 Communication User Guide

Brand: ROOTECH

Model: ACCURA 3500

Type: Communication User Guide

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ROOTECH ACCURA 3500 Communication User Guide

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