Revenue meter with integral current transformer

An integral meter and current transformer to measure single phase active and reactive energy, voltage and frequency in industrial, commercial and multi-family residential applications. The meter CT is the primary sensing element in a revenue metering system encompassing multiple meter CTs serially connected in groups in communication with data cores for collection and reporting of energy consumption. Numerous data cores may be networked to report to a central station which may be remotely interrogated over the network or dial up modem connection. The meter CT utilizes a split-core transformer with substantially overlapping fingers. Disengaging split-core sections of the meter CT enables it to be easily installed around a loaded conductor without the interruption of power to the load.

BACKGROUND OF THE INVENTION 
This invention generally relates to an apparatus and method for the 
measurement of electrical energy consumption for revenue metering and 
various other applications. 
In the past electronic kilowatt-hour meters used in revenue metering were 
discrete instruments that utilized a current transformer ("CT") with the 
meter to which it was connected being typically installed on the wall in a 
utility room. Wiring had to be installed between the meter and the 
measurement point. CTs, used to inductively sense the amount of current 
flowing through a loaded conductor, were installed in or near an adjacent 
electrical box thus requiring additional external wiring. 
A CT used in revenue metering applications typically comprises a one-piece 
toroidal coil, usually referred to as a "doughnut", which is mounted 
around a loaded conductor to be measured. Since the doughnut style CT does 
not come apart, in order to install it around a wire, the wire had to be 
disconnected so that it could be installed through the hole in the 
doughnut. Connecting a wire then, required that the electrical power had 
to be interrupted for the period of time while installation was taking 
place. In some applications this is a major problem, especially where 
uninterruptable loads, such as computers and alarm systems are involved. 
Additionally, such an interruption can be very costly especially where a 
lot of users are affected by the installation. 
Split-core type current transformers have been available for some time and 
are not novel in and of themselves. Such a design enables split sections 
of a CT to be temporarily disengaged to allow a loaded conductor to be 
surrounded by the CT when it is re-engaged. This is manifested in 
pincher-type pickups which are typically used in connection with hand-held 
ammeters. Inexpensive split-core CT designs generally employ core halves 
which merely butt together when engaged. At most, there was minimal 
overlap between split-core portions. As a result, the split-core CT's in 
the prior art are not accurate enough for revenue metering since the 
inductive coupling of the split-core CT design tended to be much more 
inaccurate than their doughnut-style counterpart. 
Additionally 3-phase meters basically required 3 single-phase meters to be 
integrated into one 3-phase meter. That meant a lot of models of dedicated 
meters had to be developed to meet all of the various applications, such 
as 3-phase, 3-element meters, 3-phase, 2-element meters, 1-phase, 
1-element and 1-phase, 2-element meters for various power applications. 
This required discrete and separate designs. 
What was needed was an accurate, split-core current transformer that could 
be easily and inexpensively installed. Additionally, it was desirable to 
have a compact CT with an integrated meter which could be combined in 
multiple-phase metering applications and which did not require a lot of 
extraneous wiring. 
SUMMARY 
An advantage of the meter CT is to measure single-phase active energy 
(kilowatt-hours), reactive energy (kilovar-hours), voltage and frequency 
in industrial, commercial and multifamily residential applications. It is 
the primary sensing element for a larger system encompassing many meter 
CTs in groups of up to 30 reporting to a single data core. Additionally, 
many data cores may be networked to a central station which may, in turn, 
be remotely interrogated over a network, phone modem connection or 
directly observed by an operator. 
The present invention solves the problems of inaccuracy associated with a 
split-core CT in revenue metering applications and that associated with 
excess wiring by moving the metering that used to be externally wired on a 
wall down into the same electrical box as the CT. One advantage of the 
invention is that it not only integrates the meter into the current 
transformer for easy and cost-effective installation, it also separates 
the sensing elements of the meter into universally adaptable metering 
components. In this respect a 2-element metering application can use 2 
meter CT's without requiring a dedicated 2-element design, a 3-element 
meter would use 3 meter CT's and so on. Thus, from a manufacturing 
standpoint, only a single style, universal meter CT product needs to be 
produced which can be combined to meet a variety of power metering 
applications. 
To overcome the accuracy problem suffered by previous split-core designs, 
the present invention utilizes a substantial interleaving of the CT's 
split-core portions. This arrangement has been demonstrated to greatly 
improve the accuracy over previous split-core designs. Thus the invention 
achieves the advantages associated with a split-core CT design without 
sacrificing accuracy. One embodiment of the present invention has been 
shown to be accurate enough for revenue metering meeting standards 
established by the American National Standards Institute ("ANSI") for 
domestic meters, and Measurement Canada, for Canadian metering 
applications. 
One advantage of the invention is that it provides for an electrical meter 
connectable to a mains voltage for computing the amount of energy being 
consumed by a load being powered by the mains voltage, comprising a 
separable housing and a split-core type current transformer within the 
housing for inductively sensing current in a conductor connected to the 
load. The transformer comprises a core of laminated metal having first and 
second sections, oppositely disposed, each of the first and second 
sections being surrounded by wound coils. A removable assembly comprising 
third and fourth sections forms an opposite side of the core and extend as 
plurality of fingers therefrom. These third and fourth sections are 
configured to be substantially the same length as the first and second 
sections and are slidably engagable with the first and second sections to 
mate forming a rectangular core having a central opening. The coils 
provide an output signal proportional to an amount of current flowing 
through the conductor located within the opening. Processing circuitry is 
located within the housing and is responsive to the output from the coils 
and the mains voltage for computing the amount of energy being consumed by 
a load connected to the conductor. Once computed, the meter provides an 
electrical output which corresponds to the amount of energy consumed or 
the voltage or frequency of the monitored voltage connected to the meter 
CT. Signal treatment circuitry is interposed between the mains voltage and 
the processing circuitry. 
Another advantage of one embodiment of the invention is the integration of 
the meter and the CT into a single, easily installable package. 
Another advantage of one embodiment of the invention is the serial 
communications circuitry that permits the meter CT to be daisy-chained 
with other meter CT's (currently 30) and tied into a single "data core", 
or concentrator for monitoring energy consumption being metered by the 
individual meter CTs. Presently, up to 30 meter CTs can be grouped into 
individual "virtual" meters, i.e., one meter CT could form one, 
single-phase meter and three meter CT's could be grouped into one, 
three-phase meter. Thus 30 meter CTs could form ten, 3-phase virtual 
meters or 30, single-phase virtual meters or any variation thereof Other 
objects and advantages of the invention will become apparent to those 
skilled in the art upon reading the following detailed description and 
upon reference to the included drawings. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a plan view of the end cap and base portions of a meter CT 
according to the present invention; 
FIG. 2 is an electrical schematic of the metering circuitry according to 
the present invention; 
FIG. 3 is an electrical schematic of the control, communications and signal 
treatment circuitry according to the present invention; and 
FIG. 4 is block diagram showing the interconnection of meter CTs in a 
network of data cores according to the present invention.

DETAILED DESCRIPTION 
Referring first to FIG. 1, an embodiment of the meter CT 10 of the present 
invention is there shown generally at 10. The meter CT 10 is shown having 
two sections, a base section 12 and an end cap section 14. Base housing 
shell and end cap housing shell 16 and 18 respectively, retain first and 
second split-core portions 20 and 22, metering printed circuit board 46 
and main printed circuit board 48. Housings 16 and 18 are preferably 
fabricated from Norell.RTM. plastic (Norell is a trademark of General 
Electric, Inc.) or its equivalent due to its durability and thermal 
characteristics. However, other plastics, such as ABS or others, may be 
utilized without substantially affecting the operation of the invention. 
First split-core portion 20 is comprised of first and second current 
transformer ("CT") sections 26 and 28, mounted in parallel to one another. 
The sections are shown to be joined together with rivets, as at 34, 
although other fastening methods may be employed. The first and second CT 
sections 26 and 28 are typically fabricated from overlapping, L-shaped 
laminated steel sections, as depicted in partial cutaway at 24. First and 
second wound coils 30 and 32 encompass first and second CT sections 26 and 
28 respectively. The purpose of coils 30 and 32 is to respond to current 
flowing through a conductor under load, as depicted at 44, by causing an 
induced current to flow through first and second wire pairs 50 and 52 
respectively to metering p.c. board 46. 
Second split-core portion 22 is comprised of third and fourth CT sections 
38, 40a and 40b, which extend in the form of matable fingers. Finger 38 
and fingers 40a and 40b are substantially the same length as first and 
second CT sections 26 and 28 and are sized to be slidably mated with them 
to form a rectangular CT with a central opening 42 when the two split-core 
portions 20 and 22 are fully engaged with one another. The split core 
portion 22 and its corresponding fingers 38, 40a and 40b are preferably 
fabricated from overlapping, ell-shaped laminated steel sections, as well. 
Both the meter CT base section 12 and its mating end cap section 14 are 
depicted in FIG. 1 without their respective cover plates (not shown). 
However, in use, the first and second split-core portions 20 and 22 would 
be fitted with cover plates as a safety precaution and to protect the 
meter CT 10 contents from environmental elements. 
Extending from metering p.c. board 46 are mains wires 54. These two wires, 
generally a white and black one, connected at points W5 and W6 on the 
metering p.c. board 46, are also connected across the electrical mains 
voltage 53 to provide the board with a voltage reference. See FIG. 2. 
Electrically interconnected to metering p.c. board 46 is main p.c. board 
48. Extending therefrom and through the side of the base housing shell 16 
is multi-colored L.E.D. 56 which is provided to give a visual indication 
as to whether the meter CT 10 has been installed with the proper polarity. 
The cover plate (not shown) of the meter CT 10 is provided with a visually 
perceivable dot (not shown) so that the meter CT may be installed in the 
proper orientation. The dot is designed to be installed facing the supply 
side of the line, however additional conventions could function equally as 
well to serve the same purpose. 
Also extending from main p.c. board 48 and through the side of the base 
housing shell 16 is communications cable 58. Cable 58 is terminated with a 
connector 60, which is preferably of a modular-type such as an RJ-45. 
Communications cable 58 sends metered information from the meter CT 10 to 
a remote data core 70 or to yet another meter CT 10. A modular receptacle 
62, is daisy-chained communicating therewith, the mate to modular 
connector 60, is provided for daisy-chaining a series of meter CTs 10 
together. Presently, thirty meter CTs 10 may be serially joined in this 
manner to communicate. 
The end cap section 14 of the meter CT 10 may be fixed into place with 
meter CT base section 12. Through holes 64a, 64b, 66a and 66b are provided 
on meter CT sections 12 and 14 enabling sealing ties or their equivalent 
to be employed to keep an assembled meter CT 10 from being separated. 
Additionally, a sensing element, such as a magnet (not shown) may be added 
to automatically sense whether the two meter CT sections 12 and 14 are 
connected. Thus, if the end cap section 14 of the split-core meter CT 10 
was removed, a change in the magnetic field would be sensed which would 
generate a signal that the CT was disconnected or tampered with, where the 
signal would be reported to the data core 70 by taking appropriate 
actions. This could be such as reporting an alarm condition or otherwise 
signaling suitable personnel that an attempt was being made to compromise 
the integrity of the meter CT 10. 
Referring next to FIG. 2, a schematic of the circuitry of the metering p.c. 
board 46 is there depicted. This board accepts a scaled signal for voltage 
and a scaled signal from the current transformer 31 for current and 
multiplies them together to produce a pulse output corresponding to 
watt-hours. Mains voltage 53 points at W5 and W 6 is provided to metering 
chip U2 via "select" resistors R10 and R11 whose values are chosen to 
scale the voltage input and which may be varied depending upon the maximum 
mains voltage 53. Various ranges may be selected, depending upon the 
maximum system voltage, nominally 150 V.sub.ac, 300 V.sub.ac and 600 
V.sub.ac. The meter CT 10 can also be adapted to accommodate various 
currents as well, such as 100 amps, 200 amps and 400 amps merely by 
properly selecting the value of resistor R5. 
Metering chip U2 performs bi-directional active and reactive power/energy 
and frequency measurements based upon sensed current through the 
split-core current transformer 31 and the mains voltage 53 supplied via 
mains wires 54 to input points W5 and W6. Preferably, metering chip U2 is 
provided as a commercially available part such as a model number SA9103C 
manufactured by SAMES. 
The metering chip U2 is a CMOS mixed signal AID integrated circuit which 
performs power/energy calculations across a power range of 1000:1 to an 
overall accuracy of better than Class 1. The metering chip U2 includes all 
the required functions for 1-phase power and energy measurement, such as 
two oversampling A/D converters for the voltage and current sensed inputs 
via W5 and W6 and current transformer 31, respectively, power calculations 
and energy integration. The metering chip U2 integrates the measured 
active and reactive power consumption into 22 bit integers, which are 
accessible via line out on the on-chip serial port. 5 Alternatively, 
metering chip U2 may be selected to provide a pulse rate output, the 
frequency of which is proportional to the power consumption being 
measured. Such a metering chip is available as a Model SA9602E from SAMES. 
When this model of the chip is employed, energy consumption may then 
determined by integrating the power measurement over time. 
In the circuit shown in FIG. 2, capacitors C4 and C6 are the outer loop 
capacitors for the two integrated oversampling A/D converters. The values 
chosen for capacitors C4 and C6 determine signal-to-noise ratio and 
stability performance and are preferably sized at around 560 picofarads. 
C3 and C5 are the inner loop capacitors of the A/D converters. The 
preferred value for capacitors C3 and C5 for the SAMES metering chip U2 is 
around 0.0033 picofarads. 
Resistors R4, R6 and R5 define the current level into the current sense 
input of metering chip U2 in the present embodiment. The values selected 
should provide an input current of 16 microamps into the metering chip U2 
at rated line current. Resistors RIO and R2 set the current for the mains 
voltage 53 sense input. The values should be selected so that the input 
current into the voltage sense input (virtual ground) is set to around 14 
microamps. Resistor R9 defines all on-chip bias and reference currents. 
The optimum value for R9 for the SAMES metering chip U2 is around 24 
kilohms. Crystal X1 is a color burst TV crystal running at 3.5795 MHz for 
the oscillator (pins 10 and 11) on the metering chip U2. The oscillator 
frequency is divided down to 1.7897 MHz on-chip to supply timing signals 
for the A/D converters and digital circuitry. 
The active and reactive energy and measured per count by metering chip U2 
may be calculated by applying the following formula: 
Energy per count=V*I/K watts seconds 
Where V=equals rated voltage 
I=rated current 
K=9281 for active energy 
K=4640 for reactive energy 
The mains voltage frequency may be calculated by the metering chip U2 as 
follows: 
Frequency=crystal frequency/register value * 8 
The metering chip U2 is provided with an on-chip serial interface for 
reading and resetting of the chip's on-chip integrators. The serial 
interface is accessed via S.sub.in and S.sub.out (pins 13 and 12) which 
are provided, in turn, to main p.c. board 48 via jumper J1. In addition to 
computing active and reactive energy, metering chip U2 can also monitor 
and consult mains voltage 53 line frequency, as well. Line frequency may 
be an important parameter, especially in those countries where the power 
is not well regulated. 
Referring next to FIG. 3, the main p.c. board 48 is therein depicted. 
Metering p.c. board 46 and main p.c. board 48 are joined by jumpers J1 and 
J2 and can be seen to be mounted at 90 degrees to one another with said 
base housing shell 16. Boards 46 and 48 communicate serially. Jumper J2 is 
connected to microcontroller U7, commercially available as a model 
PIC16C84 from MicroChip Technologies, Inc. Microcontroller U7 is an 8-bit, 
CMOS E.sup.2 PROM employing RISC (reduced instruction set) architecture. 
This model of microcontroller provides a total of 35 instructions. The 
primary function of microcontroller U7 is to read the information computed 
by the metering chip U2 and then convert, calibrate, display and transmit 
the corresponding data. The microcontroller U7 communicates through 
opto-isolators U1, U3 and U5, such as a model H11A1, from Quality 
Technologies to a serial communication port at PL2 which is, in turn, 
connected to an external data terminal or data core 70 and to supply data 
readings to the data core upon request. The microcontroller chip U7 also 
generates an output pulse which is used for factory calibration and for 
field accuracy testing. 
Employment of microcontroller U7 in this configuration is somewhat unique 
in that connections to the mains voltage 53 via points W5 and W6 are 
provided to the microcontroller U7 through resistors R10 and R11. Since 
the meter CT 10 has no transformer to galvantically isolate its output 
from the mains voltage 53 to which it is connected to, isolation is needed 
to avoid circulating current that can burn out other instrumentation which 
may be connected to the output of the meter CT. This isolation is 
accomplished via photocouplers U1, U3 and U5. In addition to adding 
safety, isolation also enables 2-element metering applications on 3-phase 
power, thus opening up new metering opportunities for suppliers. 
Another feature of the meter CT 10 is that microcontroller chip U7, has 
non-volatile memory in addition to flash memory (for programming) which 
permits the meter CT to store a calibration signal in response to a 
measured source of a precision voltage and current of a known wattage. A 
calibration constant is then serially downloaded from the data core 70 
through modular plug PL2 60 which, in turn, is stored in the non-volatile 
memory of U7, enabling the meter CT 10 to be in perfect calibration. Once 
calibrated the CT meter 10 is given a one-write digital "lock" command 
after which time the meter can no longer be programmed. The primary 
advantage of this arrangement is that there are no mechanical adjustments 
necessary to calibrate the meter CT 10, thus it is relatively unaffected 
by vibration or wear. Once calibrated and locked, recalibration is not an 
option. Thus, this one-write calibration technique also renders the meter 
CT 10 extremely tamper-resistant. 
The outputs of photocouplers U1, U3 and U5 are directed through transceiver 
U8 which converts the output levels to the standard voltage levels 
designated by RS-485 standards. Thus an output device connected to PL1 62 
sees standard RS-485 differential signal level which in this case is -0.5 
V to (Vcc +0.5 V). Transceiver U8 may be provided as a model 487CPA, low 
power, slew-rate-limited RS-485/RS-422 transceiver, available from Maxim 
Integrated Products. The low-slew-rate communication on the RS-485 bus is 
a binary protocol which is preferred in this application and other 
critical applications, such as control of traffic signals and airport 
lighting, where there is a low tolerance for error. The output of 
transceiver U8 is provided to an external device, such as a data core 70, 
via modular plug PL2 60. 
Multi-colored LED D1 is connected to suitable output pins of 
microcontroller U7. Preferably the output of LED D1 alternates between 
green and red illuminations. In this regard a green output may be used by 
the microcontroller U7 to signify that the meter CT 10 has been installed 
with the proper polarity. Microcontroller U7 may also be programmed to 
cause LED D1 to flash when the meter CT 10 is sensing power/energy. If the 
meter is connected backwards, the LED D1 will be illuminated red by 
microcontroller U7. To indicate that meter CT 10 is measuring watt-hours, 
the LED D1 will blink proportionately, either green or red, depending upon 
whether the meter CT is hooked up with the proper polarity. 
Operating voltage (d.c.) is supplied to the meter CT 10 in the form of +12 
Vdc from the data core 70 via pins W1 and W2 of plug PL2. This voltage is 
used to power the RS-485 communication ports, PL1 and PL2 and is also 
stepped down, isolated and regulated to +5 V.sub.dc for the 
microcontroller chip U7 and the metering chip U2. This step down function 
is performed by a DC to DC converter U4. Regulation is accomplished via 
high isolation voltage regulator U6, as may be commercially supplied as a 
model HPR 400 by Power Convertibles. To conserve on space, voltage 
regulator U6 may be provided as a single-in-line package (SIP). 
Referring additionally to FIG. 1, a nominally three foot (3') 
communications cable 58 is provided having an RJ-45-type modular plug 60 
and is labeled generally in FIG. 3 as W1-W8. A mating RJ-45-type 
receptacle 62 is employed at PL1, enabling numerous meter CTs, as at 10, 
to be daisy-chained together by interconnecting the PL1 and PL2 components 
of respective meter CTs. The last meter CT in a daisy-chain is then 
connected to the external data concentrator or data core 70 via 
communication cable 58 and modular plug 60. It should be appreciated that 
in some applications other connectors or hard-wired arrangements may be 
preferable to the modular ones depicted herein. 
The communications between the meter CT 10 and data core 20 is a binary 
protocol which is quite sophisticated and comprises a series of messages 
and responses to messages. Commands developed for the meter CT 10 follow 
below. During the manufacturing process communication takes place between 
the meter CT 10 and a calibration test stand (not shown). This is for 
testing and calibration. Once tested and calibrated, the meter CT 10 is 
given a "lock" command, and will no longer accept external calibration 
commands. Following testing, that is during normal operations, 
communications is between the data core 70 and the meter CT 10. The 
communication does not require a data core 70, as a user may interface 
with a meter CT 10 with a personal computer, or other computing device, 
given the proper protocol interface. 
The communications between the meter CT 10 and the data core 70 may be 
conducted at 9600 baud, with 8 bits, no parity, one start bit and one stop 
bit, although any number of communications speeds and protocols may be 
equally suited. There are provided, as disclosed below, a series of 
commands and responses to perform various functions and to store and 
retrieve watt-hour readings. In some applications it may be necessary to 
synchronize with other CT 10 meter readings, especially when conducting 
demand calculations. Therefor, a "freeze and hold" command is provided 
which causes the meter CT 10 to take a reading and store it for later 
transfer to a requesting device, such as a data core 70. 
All communications is accompanied by a check byte to make sure that all 
communications have been transmitted in a reliable manner. Using a check 
byte, the sender of data computes a value based upon the data being sent. 
The receiver, using the same algorithm, calculates a value based upon the 
data which was received. The two values are then compared to determine the 
integrity of the data. If the two values are identical, the receiver can 
have some assurances that the information received is the same as the 
information sent. Following is a complete listing of different commands. A 
calibration constant can be sent to the meter CT 10 and then the 
calibration constants may be read from meter CT. Each meter CT 10 is 
provided with a unique electronic serial number stored in non-volatile 
memory and that serial number can be read by data core 70 or other reading 
device. 
Multiple data cores, as at 70, may be wired to communicate with a central 
p.c. 72 which may be interrogated over a network connection, modem line as 
at 74 or directly observed via a monitor 73. 
Meters are referred to as "slaves" because they never originate a 
communication without a request from the "master" (data core 70). Slave 
meters are polled by the "master" (data core 70) using the protocol and 
commands herein defined. Slaves listen for approximately 120 mSec and are 
busy for approximately 40 mSec each internal read cycle of 160 mSec. 
The Transport Protocol used by the meter CT 10 is a variation of HDLC 
master/slave messaging system. 
Serial Communication Parameters: 9600 BAUD, 8 bit, no parity, 1 start bit, 
1 stop bit 
Message Structure: All messages conform to the same general format, as 
follows. 
__________________________________________________________________________ 
START CHARACTER 
7E HEX (126 DEC.) 
DESTINATION ADDRESS 
ADDRESS OF DEVICE INTENDED TO RECEIVE 
MESSAGE (00 TO FE HEX, 0 TO 254 DEC) 
00 HEX IS RESERVED AS A BROADCAST (GLOBAL) 
ADDRESS, FF HEX IS THE MASTER ADDRESS 
SOURCE ADDRESS 
ADDRESS OF METER OR MASTER SENDING THE 
MESSAGE 
FUNCTION CODE 
COMMAND BYTE AND EXTENSION 
(2 BYTES) 
[DATA] OPTIONAL DATA FIELD OF 1 TO 3 BYTES. SOME 
COMMANDS CONTAIN DATA AS DEFINED BY 
THE FUNCTION CODE. 
CHECK BYTE A SINGLE BYTE CHECKSUM OF ALL MESSAGE 
BYTES BEGINNING WITH THE FIRST BYTE FOLLOWING 
THE START CHARACTER AND ENDING WITH THE BYTE 
PRECEDING THE CHECKSUM CHARACTER 
STOP CHARACTER 
7E HEX (126 DEC) 
__________________________________________________________________________ 
The start/stop character is intended to be a unique character, therefore, 
any such character naturally occurring in the message content is modified 
to maintain the uniqueness by simply implementing the following rules. 
Any transmitted character which is not a START or STOP character is 
modified to prevent an unintended START/STOP character. The value is 
changed and an additional byte is added: 
7E Hex replaced by 7D 01 Hex 
7D Hex replaced by 7D 02 Hex 
The receiving device will interpret received characters within the message 
by the same rules: 
7D 01 Hex represents a true value of 7E Hex 
7D 02 Hex represents a true value of 7D Hex 
Transport Character Modification is the last process before transmission 
and the first process of reception (after detection of a valid start 
character). 
Meter CT Communication Functions 
__________________________________________________________________________ 
Function Code 
Hex Bytes 
CMD EXT 
Function Action Taken 
__________________________________________________________________________ 
45 01* 
Read Exception Status 
Communication response of meter 
status (error codes) 
46 NN Freeze Holding Registers 
Command to meter(s) to update registers 
4C 01 Lock Meter Prevents any future calibration changes to 
meter (calibration, Ser. No. & parameters 
4D 01 Read Meter Calibration 
Communication response containing 
meter calibration value 
51 01 Query Meter ID 
Communication response of meter(s) 
identification parameters 
52 01 Read Holding Watt-hour 
Communication response of metered 
Register Values 
watt hour quantity 
54 01 Begin Test Mode 
Commands meter to output test pulses 
57 01 (L) Write Meter Calibration 
Writes calibration constant to the meter 
57 02 Write Meter Address 
Writes new address value into the meter 
57 03 (L) Write Meter Ser. No. 
6 hex characters are written to the 
addressed meter 
57 04 (L) Write Voltage Rating 
Sets meter full scale voltage 
57 05 (L) Write Current Rating 
Sets meter full scale current 
58 01 Exit Test Mode 
Commands meter to exit test mode if 
active. The meter also exits Test Mode 
on loss of supply voltage, or receiving 
any bus communications with 
destination address of another meter. 
.circle-solid. (L) = Function disabled by Lock Meter Command 
* Functions planned but not yet implemented. 
__________________________________________________________________________ 
COMMANDS AND RESPONSES 
[45 01] READ EXCEPTION STATUS 
HEX BYTE 
__________________________________________________________________________ 
7E START CHARACTER 
01 METER ADDRESS (DESTINATION) 
FF MASTER ADDRESS (SOURCE) 
45 FUNCTION CODE 
01 FUNCTION EXTENSION 
XX CHECK BYTE 
7E STOP CHARACTER 
__________________________________________________________________________ 
RESPONSE TO READ METER EXCEPTION STATUS [45 01] 
HEX BYTE 
__________________________________________________________________________ 
7E START CHARACTER 
FF DESTINATION ADDRESS IS MASTER 
01 SOURCE ADDRESS OF METER RESPONDING 
45 FUNCTION CODE (ECHO OF CMD RECEIVED) 
01 COMMAND EXTENSION 
00 DATA BYTE REG 1 HI 
00 DATA BYTE REG 1 LO 
XX CHECK BYTE 
7E STOP CHARACTER 
Each bit of data field corresponds to a possible error condition 
00 HEX (no bits set) indicates no error conditions. 
__________________________________________________________________________ 
[46 NN] FREEZE HOLDING REGISTERS (BROADCAST ADDRESS) 
HEX BYTE 
__________________________________________________________________________ 
7E START 
00 BROADCAST ADDRESS DESTINATION 
FF SOURCE ADDRESS IS MASTER 
46 FUNCTION CODE IS A COMMAND FREEZE 
03 FUNCTION EXTENSION USED AS A 
SEQUENCE NUMBER e.g., (03) 
XX CHECK BYTE 
7E STOP CHARACTER 
__________________________________________________________________________ 
The Command Extension byte is used as a sequence number for coordination of 
the freeze/read communications. The response to a read following a freeze 
command will include the last freeze sequence number executed. The master 
(Data Core) 70 can use this information to verify that a meter CT 10 is on 
the current read/freeze cycle. Multiple freeze commands are sent to insure 
a high probability of success on each freeze/read cycle. Meter CTs 10 will 
not execute a freeze command if it contains the same sequence number as 
the previously executed freeze. 
______________________________________ 
RESPONSE TO FREEZE HOLDING REGISTERS [46 NN]-NONE 
[4C 01] LOCK METER 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
FF METER ADDRESS (DESTINATION) 
01 MASTER ADDRESS (SOURCE) 
4C FUNCTION CODE 
01 FUNCTION EXTENSION 
XX CHECK BYTE 
7E STOP CHARACTER 
______________________________________ 
RESPONSE TO LOCK METER [4C 01]-NONE 
[4D 01] READ METER CALIBRATION 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
01 METER ADDRESS (DESTINATION) 
FF MASTER ADDRESS (SOURCE) 
4D FUNCTION CODE 
01 FUNCTION EXTENSION 
XX CHECK BYTE 
7E STOP CHARACTER 
______________________________________ 
RESPONSE TO READ METER CALIBRATION [4D 01] 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
FF DESTINATION ADDRESS IS MASTER 
01 SOURCE ADDRESS OF METER RESPONDING 
4D FUNCTION CODE (ECHO OF CMD RECEIVED) 
01 COMMAND EXTENSION 
09 DATA BYTE 1 
FA DATA BYTE 2 
XX CHECK BYTE 
7E STOP CHARACTER 
______________________________________ 
[51 01] QUERY METER ID 
HEX BYTE 
______________________________________ 
7E START CHARACTER FROM MASTER 
01 ADDRESS 
FF SOURCE ADDRESS 
51 FUNCTION CODE 
01 FUNCTION EXTENSION 
XX CHECK BYTE 
7E STOP CHARACTER 
______________________________________ 
RESPONSE TO QUERY METER ID [51 01] 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
FF ADDRESS OF MASTER 
01 ADDRESS OF METER 
51 FUNCTION COMMAND (ECHO OF 
COMMAND RECEIVED) 
01 FUNCTION EXTENSION 
12 SN BYTE 1 
34 SN BYTE 2 
56 SN BYTE 3 
00 VOLT RTG, BYTE 1 
78 VOLT RTG, BYTE 2 
00 AMP RTG, BYTE 1 
64 AMP RTG, BYTE 2 
01 METER TYPE 
65 FIRMWARE VER 101(65HEX) 
XX CHECK BYTE 
7E STOP CHARACTER 
______________________________________ 
[52 01] READ HOLDING REGISTERS Master Read Command to 
specific address 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
01 ADDRESS OF METER TO READ 
FF SOURCE ADDRESS IS MASTER 
52 FUNCTION CODE IS A COMMAND READ 
HOLDING REGISTERS 
01 FUNCTION EXTENSION 
XX CHECK BYTE 
7E STOP CHARACTER 
* suggested (POSSIBLE) use of function extension is to select which 
register to read such as: 01 = WH, 02 = VARH, 03 = VOLTHOURS, 
04 = FREQ, OA = ALL 
______________________________________ 
RESPONSE TO READ HOLDING REGISTERS [52 01] 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
FF DESTINATION ADDRESS IS MASTER 
01 SOURCE ADDRESS OF METER RESPONDING 
52 FUNCTION CODE IS A COMMAND READ 
(ECHO OF CMD RECEIVED) 
NN COMMAND EXTENSION IS SEQUENCE 
NUMBER OF PREVIOUS FREEZE 
01 DATA BYTE 1 
1A DATA BYTE 2 
XX CHECK BYTE 
7E STOP CHARACTER 
______________________________________ 
[54 01] ENTER METER TEST MODE 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
01 METER ADDRESS (DESTINATION) 
FF MASTER ADDRESS (SOURCE) 
54 FUNCTION CODE 
01 FUNCTION EXTENSION 
XX CHECK BYTE 
7E STOP CHARACTER 
______________________________________ 
RESPONSE TO ENTER METER TEST MODE [54 01]-NONE 
[57 01] WRITE METER CALIBRATION 
______________________________________ 
7E START CHARACTER 
01 METER ADDRESS (DESTINATION) 
FF MASTER ADDRESS (SOURCE) 
57 FUNCTION CODE WRITE MEMORY 
01 FUNCTION EXTENSION (Identifies 
which parameters to be written) 
09 DATA BYTE 1 
FA DATA BYTE 2 
XX CHECK BYTE 
7E STOP CHARACTER 
______________________________________ 
RESPONSE TO WRITE METER CALIBRATION [57 01]-NONE 
[57 02] WRITE METER ADDRESS (UNIT ID) 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
01 METER ADDRESS (DESTINATION) 
FF MASTER ADDRESS (SOURCE) 
57 FUNCTION CODE WRITE MEMORY 
09 FUNCTION EXTENSION (Identifies 
which parameters to be written) 
FA NEW ADDRESS 
XX CHECK BYTE 
7E STOP CHARACTER 
* AA Is a single 8 bit byte represented as 2 hex characters. 
Possible values are 1 to 254 decimal (FE HEX). 00 is reserved for 
a broadcast address and FF (255) is the address of the master. 
______________________________________ 
RESPONSE TO WRITE METER ADDRESS [57 01]-NONE 
[57 03] WRITE METER SERIAL NUMBER 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
01 METER ADDRESS (DESTINATION) 
FF MASTER ADDRESS (SOURCE) 
57 FUNCTION CODE WRITE MEMORY 
03 FUNCTION EXTENSION (Identifies 
which parameters to be written) 
00 DATA BYTE 1 
01 DATA BYTE 2 
08 DATA BYTE 3 
XX CHECK BYTE 
7E STOP CHARACTER 
Example serial number is 00 01 08 HEX, 264 DECIMAL. 
______________________________________ 
RESPONSE TO WRITE METER SERIAL NUMBER [57 03]-NONE 
[57 04] WRITE METER VOLTAGE RATING 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
01 METER ADDRESS (DESTINATION) 
FF MASTER ADDRESS (SOURCE) 
57 FUNCTION CODE WRITE MEMORY 
04 FUNCTION EXTENSION (Identifies 
which parameters to be written) 
00 DATA BYTE 1 
78 DATA BYTE 2 
XX CHECK BYTE 
7E STOP CHARACTER 
Example voltage rating is 00 78 HEX,120 decimal. 
______________________________________ 
RESPONSE TO WRITE METER VOLTAGE RATING [57 04]-NONE 
[57 05] WRITE METER CURRENT RATING 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
01 METER ADDRESS (DESTINATION) 
FF MASTER ADDRESS (SOURCE) 
57 FUNCTION CODE WRITE MEMORY 
05 FUNCTION EXTENSION (Identifies 
which parameters to be written) 
00 DATA BYTE 1 
64 DATA BYTE 2 
XX CHECK BYTE 
7E STOP CHARACTER 
Example current rating is 00 64 HEX, 100 decimal. 
______________________________________ 
RESPONSE TO WRITE METER CURRENT RATING [57 05]-NONE 
[58 01] EXIT METER TEST MODE 
HEX BYTE 
______________________________________ 
7E START CHARACTER 
01 METER ADDRESS (DESTINATION) 
FF MASTER ADDRESS (SOURCE) 
58 FUNCTION CODE 
01 FUNCTION EXTENSION 
XX CHECK BYTE 
7E STOP CHARACTER 
______________________________________ 
RESPONSE TO ENTER METER TEST MODE [58 02]-NONE 
______________________________________ 
A check byte is a single byte transmitted at the end of each message for 
error detection. The check byte is calculated by successive exclusive-OR 
operations on all bytes of the message beginning after the START 
characters (7E HEX) and including the last byte prior to the check byte. 
Inserted data modifiers are not included in the check byte calculation. 
Checkbyte calculations are unaffected by the START/STOP character 
processing. To clarify, on transmission the checkbyte is calculated before 
START/STOP processing and on reception checkbyte calculation is done after 
START/STOP processing. So, even if the checkbyte is modified for 
transmission it will be returned to its original value by the receiver 
before testing. 
Starting with the first byte after the START character, begin by exclusive 
ORiing with the next byte, then exclusive or that result with the next 
byte until finished. The example used is a meter CT 10 response to a read 
meter calibration command. 
Check Byte Calculation Example 
______________________________________ 
HEX BINARY 
______________________________________ 
7E START CHARACTER 
FF 1111 1111 
01 0000 0001 
4D 0100 1101 
01 0000 0001 
09 0000 1001 
FA 1111 1010 
41 0100 0001 CHECKSUM RESULT 
7E STOP CHARACTER 
______________________________________ 
Each command is a 2 byte command that has a command portion in the 
left-hand portion of the command. The extension byte is a breakdown of 
that command. The meter CTs 10 current and voltage rating are also stored 
in memory such that the data core 70 can query each meter CT in a chain 
and read each of their unique identities and ratings to determine whether 
each is a 100 amp, 150 V meter, etc. This may be helpful in the event 
that, if someone changes or otherwise tampers with the meter CT 10, data 
core 70 will be able to determine the change and, if appropriate, report 
the change. 
Accordingly, it is apparent from the foregoing detailed description and 
illustrative drawings that an integrated meter CT has been invented which 
satisfies the objectives and achieves the advantages stated throughout 
this specification. While the invention is susceptible to various 
modifications and alternative forms, specific embodiments thereof have 
been shown by way of example in the drawings and have herein been 
described in detail. It should be understood, however, that it is not 
intended to limit the invention to the particular forms disclosed, but, on 
the contrary, the intention is to cover all modifications, equivalents, 
and alternatives falling within the spirit and scope of the invention as 
described by the appended claims.