WO1992009899A1

WO1992009899A1 - Display for a circuit breaker trip unit

Info

Publication number: WO1992009899A1
Application number: PCT/US1991/009000
Authority: WO
Inventors: Andy Allen Haun; Earl John Tessmer
Original assignee: Square D Company
Priority date: 1990-11-30
Filing date: 1991-11-27
Publication date: 1992-06-11
Also published as: AU9102191A; EP0513319A1; EP0513319A4; MX9102320A; CA2074264A1

Abstract

A portable communication device communicates with a circuit breaker trip unit in a cost-efficient, power-effective manner. The portable communication device includes a keypad (10, 12), a display (78), an interface circuit (16) which couples data sent from the trip unit with the portable communication device, a microcomputer (13) which responds to the keypad (10, 12) and to the data sent from the trip unit for controlling the display (78), a local power source which provides power to the portable communication device, and a power switch which is responsive to the microcomputer for disabling the local power source during periods when data is not being received from the trip unit. The microcomputer may be arranged to directly control the power switch. In this manner the microcomputer can command the power switch to disable the local power when the absence of data from the trip unit indicates that power to the portable communication device is not needed.

Description

DISPLAY FOR A CIRCUIT BREAKER TRIP UNIT

Field Of The Invention

The present invention relates generally to circuit breaker trip units and, more particularly, to peripheral display devices communicating with circuit breaker trip units.

Background Of The Invention

The practice of monitoring circuit breaker trip units is becoming

increasingly important. Proper monitoring can provide tangible benefits with respect to equipment operation and maintenance; therefore, significant return on investment. More specifically, these benefits include

savings in terms of equipment energy costs and maintenance costs, better equipment utilization, and increased system reliability.

Known monitoring techniques have included a number of display units coupled to circuit breaker trip units. For instance, fixed display units have been permanently affixed as part of the circuit breaker housing. Unfortunately, this technique is disadvantageous in applications having a multitude of circuit breakers because of the cumulative cost of each display unit in each circuit breaker housing.

Similarly disadvantageous is the remotely located display unit which is cabled to a multitude of circuit breaker trip units. This type of implementation is costly in terms of the excessive cables that are required

to interconnect the system, and of the labor that is required to install such a system. Moreover, in many applications a remotely located display unit is not practical for monitoring and servicing the circuit breaker system.

In another known monitoring technique, a portable display unit is configured to draw power from the circuit breaker trip unit. This technique is advantageous in that it overcomes many of the problems associated with the previously discussed techniques, but is disadvantageous in applications which require monitoring of the trip unit during system down times; that is, when the trip unit has experienced instantaneous or longer periods of power interruption. During these times, when power to the trip unit is interrupted, power to the display unit is also interrupted.

Summary of the Invention

It is a general object of the present invention to provide a reliable, power conservative system for monitoring the operation of a circuit breaker trip unit.

It is a more specific object of the present invention to provide such

a system that can be easily retro-fit with existing circuit breaker arrangements.

In accordance with a preferred embodiment, the present invention provides a portable communication device for communicating with a circuit breaker trip unit, in which the portable communication device includes a keypad, a display, an interface circuit which couples data sent from the trip unit with the portable communication device, a control circuit which responds to the keypad and to the data sent from the trip unit for controlling the display, a local power source which provides power to the portable communication device, and a power switch which is responsive to the control circuit for disabling the local power source during periods when

data is not being received from the trip unit.

Brief Description Of The Drawings

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

FIG. la is a schematic diagram of a portable communication device, in accordance with the present invention, for monitoring a circuit breaker trip system;

FIG. lb is a perspective view diagram of the portable communication device shown in FIG. la; and

FIGS. 2-7 comprise a flow chart illustrating a preferred manner in which the microcontroller of FIGS, la and lb may be programmed. While the invention is susceptible to various modifications and alternative forms, a specific embodiment thereof has been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed. On the contrary, the intention is to cover all

modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. Description Of The Preferred Embodiments

The present invention is particularly useful in industrial applications

wherein a plurality of circuit breaker trip units are periodically monitored and serviced. In such an environment, the portability of the present invention allows it to be interconnected with each trip unit sequentially so as to minimize the number of components.

In FIG. la, a preferred embodiment of the present invention is shown in schematic form to include a pair of push buttons 10 and 12 implementing a simple keypad, a display circuit 14, an interface circuit 16 coupling data sent from a circuit breaker trip unit (not shown), a microcontroller 18 and a power control circuit 20.

The microcontroller 18, which is preferably implemented using a Motorola 68HC705C8-type IC (integrated circuit), operates as the control center for the portable communication device illustrated in FIG. 1. The microcontroller 18 receives both user and trip unit type data. User data is received by the microcontroller 18 via push buttons 10 and 12, using pull¬ down 100 kOhm resistors 22-23 and a menu driven computer program (FIGS. 2-7). Trip unit data is received by the microcontroller 18 at a peripheral port (e.g., PD0) via the interface circuit 16, which includes a fiber optic connector 26 for electrically isolating the portable communication device of FIG. la from the trip unit, a 100 kOhm

termination resistor 28 and conventional amplification circuitry for conditioning the trip unit data for reception by the microcontroller 18. The amplification circuitry includes a pair of operational amplifier circuits and a transistor circuit. The operational amplifier circuits, which may both be implemented using LM358-type ICs, include an inverting amplifier 30 and a conventional negative feedback amplifier 32. The resistor 34 in the feedback path of the inverting amplifier 30 may be implemented using a 1.5 mega-Ohm resistor, and the amplification for the

amplifier 32 may be implemented using a 470 kOhm resistor 36 and a 10 kOhm resistor 38. The final stage of the interface circuit 16 includes a

BS170 type FET (field-effect transistor) 40 and bias resistors 42 and 44 having 10 kOhm and 100 kOhm values, respectively.

The power control circuit 20 is another important part of the portable communication device of FIG. la. It allows the user to power-on the portable communication device via momentary push-button switch 50, and allows the microcontroller 18 to automatically power-down the portable communication device in the event that the microcontroller 18 does not receive data from the trip unit for a prescribed period of time. This significantly extends the life of the power source (battery 52) for the portable communication device in that it maximizes its efficiency.

More specifically, diode 54 is momentarily forward biased upon

power-up, via push-button switch 50, to allow a FET 56 to engage a bipolar transistor 58, which in turn drives an LP2950 type five-volt regulator 60 to provide Vcc power, using a 0.1 microFarad capacitor 62 to suppress noise. The FET 56 may be implemented using a BS170 type component, the transistor 58 using a 2N3906 type component and resistors 64, 66 and 68 using 100 kOhm, 27 kOhm and 10 kOhm values, respectively. Once the microcontroller 18 receives operating power, it drives line 72 high (via port PA1) to forward bias a diode 74, which continues to allow the FET 56 to engage the bipolar transistor 58 so as to maintain Vcc. The microcontroller 18 then employs a software timer to time periods during which no data is received by the trip unit. If the duration exceeds a prescribed limit, the microcontroller 18 drives line 72 low to disengage the bipolar transistor 58 and power-down the portable communication device so that power from the battery is not wasted.

The display circuit 14 is controlled conventionally, using the PB0-

PB7 peripheral ports of the microcontroller 18 to drive a 4 by 16 LCD

(liquid crystal display) 78, which is preferably implemented using an LM73X4C16CX type component available from Densitron. A negative voltage generator 80, such as an Intersil ICL7660 component, in conjunction with a pair of 10 microFarad capacitors 82 and 84, is used to provide the requisite negative voltage to the LCD 78. Resistors 86 and 88 may be implemented using a number of different values depending on the desired brightness of the LCD 78. In one application, for example, 4.7k kOhm and Ik kOhm values may be used for resistors 86 and 88, respectively.

FIG. lb illustrates a preferred embodiment of the portable

communication device from a perspective view. The device includes an enclosed housing 90, an optical waveguide 92, a battery compartment 94, and the switches 10, 12, 50, the display 78 and the connector 26, discussed above in connection with FIG. la.

FIGS. 2-7 comprise a flow chart for implementing the

microcontroller 18 of FIG. 1. More specifically, FIG. 2 represents a flow

chart for the main operating program of the microcontroller. FIGS. 3 and 5 constitute respective flow charts for interrupt routines which are respectively serviced in response to a timer which is internal to the microcontroller and in a response to data being received from the trip unit via the SCI port of the microcontroller. The remaining charts depicted in

FIGS. 4 and 6-7 are subroutines which are respectively called in response to the reception of data messages, for periodically looking for keypad data

and for periodically controlling the display.

The flow chart of FIG. 2 begins upon power-up as depicted at block 100. At blocks 102 and 104, the microcontroller initializes its various ports and system variables, including driving the output line (72 of FIG. la), which maintains the local power source in the "on" condition.

At block 106, the microcontroller performs a test to determine if its SCI data register is full. If the SCI data register is full, flow proceeds from block 106 to block 108 where the subroutine of FIG. 4 is serviced. Upon

returning from the subroutine of FIG. 4, or from block 106 if the SCI data register is not full, flow proceeds to block 110.

At block 110, the microcontroller performs a test to determine if the display reset timer has timed out. The display reset timer from block 110 and other timers to be discussed in connection with this flow chart of FIG. 2 are controlled using the interrupt service routine of FIG. 3. The display reset timer is used to indicate when the display (78 of FIG. la) is

ready to be controlled after power-up, since a 15 millisecond post-power- up delay is specified for the preferred LCD component. Accordingly, if the display reset timer is equal to 0, then the 15 millisecond delay has elapsed, and the microcontroller proceeds to block 112 to reset the LCD in preparation for subsequent use and to disable the timer.

At block 114, the microcontroller determines whether or not it is time to service the keypad. A keypad service timer, which is also maintained using the interrupt service routine of FIG. 3, is regularly decremented until it reaches 0, at which time the microcontroller proceeds to determine if any data had been entered via the keypad. Thus, at block

116 the microcontroller performs a test to determine if all the keys have been serviced. This is determined by checking if the key-ready flag is set (see FIG. 6). If all the keys have been serviced, flow proceeds to block

118 where the microcontroller calls the keypad service subroutine of FIG.

6. From block 118, or if all the keys have not been serviced at block 116, flow proceeds to block 120 where the keypad service timer is restored to its original value. From block 120, flow proceeds to block 122. At block 122, a test is performed to determine if the display reset timer has been disabled. If the display reset timer has been disabled, then the 15 millisecond delay after power-up has elapsed, and flow can proceed to block 124 where the display service subroutine of FIG. 7 is called for servicing the LCD. At block 126, a test is performed to determine if the prescribed time period, during which no trip data has been received, has lapsed. A shut down timer, controlled by the routine of FIG. 3, is used for this purpose as depicted in block 126. If that prescribed period has lapsed, flow proceeds to block 128 where the appropriate power control bit (line 72) is set low to shut down power to the portable communication device. From block 128, or in response to the shut down timer not being decremented to 0, flow returns to block 106.

The timer interrupt service routine, which is depicted in FIG. 3, occurs each millisecond. The flow chart begins at block 132 and, at block 134, the microcontroller sets the output compare register to interrupt at the next millisecond.

At blocks 136, 138 and 140, the display-reset, keypad service and

125-millisecond timers are decremented. The 125-millisecond timer is used to decrement the shut-down timer and the display timer, which have

relatively long time periods. At block 142, the microcontroller performs a test to determine if the 125-millisecond timer has been decremented to 0. If so, the 125-millisecond timer is refreshed and flow proceeds to blocks 144 and 146 to decrement the display and shut-down timers. From block 146, and from block 142 if the 125-millisecond timer has not been decremented to 0, flow proceeds to block 148, where the microcontroller executes a return from interrupt command.

FIG. 4 illustrates a preferred manner of implementing block 108 of FIG. 2: the SCI data subroutine. The subroutine is entered at block 152, and, at block 153, the microcontroller interprets the data packet received via the SCI port. The received data packet may be related to

configuration data or operating-status data. Each such type of data corresponds to the type of multi-byte packet that is being sent from the trip unit. For further information concerning the data packet structure, reference may be made to copending U.S. Patent Application No.

07/503,267, filed on April 2, 1990, incorporated in its entirety by reference. If the received data is configuration data, flow proceeds from block 153 to block 154 where the configuration data memory locations are updated. If the received data is not configuration data, flow proceeds from block 153 to block 155 where a test is performed to determine if it is status data. If so, the status data memory locations are updated at block 156. At block

157, the microcontroller updates its record of the trip status. As discussed in the above copending application, the trip status includes long time trip, short time trip, instantaneous trip, ground fault trip and normal operation.

At block 158, the microcontroller clears the SCI data ready flag so that it can be informed the next time a data packet has been received via the SCI port. The microcontroller then executes a return from subroutine command, as depicted in block 160.

FIG. 5 illustrates the SCI interrupt routine, which is serviced each time a byte is received via the SCI port. Upon entering the routine at block 164, the microcontroller performs a test to determine if any errors have been received, depicted at block 166. If one or more errors were

received via the SCI port, flow proceeds from block 166 to block 168 where the microcontroller resets the SCI port and an associated message

byte counter, which is used to track how many bytes of a particular packet had been received so that errors are not accumulated. From block 168, flow proceeds to block 170 where the microcontroller refreshes the shutdown timer, since data has been received from the trip unit, and the portable communication device of FIG. la need not be powered down.

From block 170, flow proceeds to block 172 where the microcontroller executes a return from interrupt command. If errors are not detected via block 166, flow proceeds to block 174 where a test is performed to determine if the received data byte constitutes the beginning of a data message. If not, flow proceeds to block 176 where the microcontroller stores the data byte and increments the data byte counter in order to track the number of received bytes in the instant packet. From block 176, flow proceeds to block 178 where a test is performed to determine if the received byte constitutes the end of a data message or packet. If the received byte does constitute the end of a data message, flow proceeds to block 180 where a test is performed to

determine if there are any byte or bit errors in the packet that has been received. This is preferably done by performing a conventional checksum test. If the checksum test passes, flow proceeds to block 182 where the microcontroller sets the SCI data ready flag of block 158 (FIG. 4) to record that a packet has been received. From block 182, flow proceeds to previously discussed block 168.

If the microcontroller determines that the received byte is the beginning of a data message or packet, flow proceeds from block 174 to block 184 where the microcontroller begins to form the packet by storing the beginning of the message and resetting the byte counter indicating the number of bytes that have been received for the packet. From block 184, from block 178 if the received byte constitutes the end of a data message and from block 180 if the checksum test fails, flow proceeds to block 170 to refresh the shutdown timer before returning from the interrupt routine. FIG. 6 illustrates the keypad service subroutine depicted in block 118 of FIG. 2. After entering the routine at block 188, flow proceeds to block 190 where the microcontroller reads the port at which the keypad

(set of push-button switches) is connected. At block 192, the microcontroller determines if a push-button switch has been depressed or released by comparing the present state of the push-button switch port to its previous state. If the present and the previous states of the push-button switch port are the same, flow proceeds from block 192 to block 194 where the microcontroller executes a return from subroutine command.

If the microcontroller determines that a push-button switch has been depressed or released, flow proceeds from block 192 to block 196 where the microcontroller once again reads the same port. At this point in the flow chart, the microcontroller initiates a switch debouncing procedure.

If the microcontroller reads the push-button switch port three times and concludes that the data in the port has not changed at each one of the three reads, then the switch has been debounced. Thus, from block 196, flow proceeds to block 198 where the microcontroller makes the first comparison. From block 198, flow proceeds to block 200 if the successive data port reads are not the same.

At block 200 a counter, which is used for tracking the number of times the comparison has been made, is cleared. If the success reads at block 198 are the same, flow proceeds from block 198 to block 202 where the counter is incremented.

From block 202, flow proceeds to block 204 where a test is performed to determine if three successive reads have taken place with the same data being read at the port. If not, flow returns from block 204 to

block 196 for the next successive read of the push-button switch port. From block 204, flow proceeds to block 206 where a test is performed to determine if the push-button switch has been released. If the push-button switch has been released, flow proceeds to block 208 where the microcontroller updates a register storing the status of the

associated push-button switch and sets a key ready flag to record that a switch has been pressed and released, the latter of which must happen for the microcontroller to act on the data input by the user. From block 206, if the switch has not been released by this time, flow proceeds to block 194 where the microcontroller executes a return from subroutine command.

FIG. 7 illustrates the display service subroutine which is depicted at block 124 of FIG. 2. The subroutine of FIG. 7 changes information on the display in response to: the 500 millisecond timer timing out, a user request via the keypad, or trip unit data requiring a change. Preferably, there are two types of display modes, a current-related mode and a configuration mode with six subtypes associated with the configuration mode. The current-related information mode displays the amperage for each of three phases plus ground fault. The configuration submodes display: (1) identification of breaker type, current sensor size and amperage rating; (2) long time trip settings, pick-up settings in amperes and in time; (3) short- time trip settings, pick-up settings in amperes and in time; (4)

instantaneous trip settings and associated pick-up settings; (5) ground fault trip settings and associated pick-up settings; and (6) the revision number

for the hardware and firmware.

After entering the subroutine at block 210 of FIG. 7, flow proceeds to block 212 to determine if a flag has been set, which flag indicates that another portion of the display needs to be written. Only one portion of the display is written at a time. If other portions of the display have not been written, then the display is still in progress. If another display portion needs to be written, flow proceeds from block 212 to block 214 where the microcontroller updates the display using conventional line-by-line LCD writing techniques. From block 214, flow proceeds to block 216 where the microcontroller performs a return from subroutine command.

From block 212, flow proceeds to block 218 if a display update is not in progress to determine if the key-ready flag is set (see block 208 of FIG. 6). If the key-ready flag is set, then a key or switch was detected as being depressed and released, and flow proceeds to block 220.

If the key-ready flag is not set, flow proceeds from block 218 to block 222 where the microcontroller performs a test to determine if current-related information is being displayed; for example, the display of current in each of the three phases and ground fault.

If the display is not displaying current-related information, flow proceeds from block 222 to block 224 where the microcontroller performs a test to determine if the display is displaying configuration information and the configuration requires changing. If at least one of these conditions is not met, no further action is necessary and flow proceeds to block 216 for exiting the subroutine. If both of these conditions are met, flow proceeds from block 224 to block 226 where the microcontroller sets up for writing the new configuration. This may be done by writing a portion of the new display during this visit to the display service routine and the remaining portion during the next visit. From block 226, flow proceeds to block 214 for writing the new configuration data on the display.

From block 222, flow proceeds to block 228 if the information being displayed is current-related information. At block 228, the current-related

information is set for being updated (or refreshed) by setting a flag to record that updates should only pertain to the numbers, e.g., the displayed amperages for the various phases and ground fault. This updating or refreshing in the display mode for "current" is set to occur every 500 milliseconds. From block 228, flow proceeds to block 214 for the actual refreshing of the current-related information on the display.

At block 220, if the push-button switch corresponding to a function key is detected as being depressed and released, flow proceeds to block 232 where the microcomputer toggles the display from the configuration- type display to the current-related information display or vice-versa. From block 232, flow proceeds to block 214 where the display is actually written to for the change indication of block 232.

From block 220, flow proceeds to block 233 if the function switch was not engaged. At block 233, a test is performed to determine if current-related information is being displayed. If so, engagement of the other switch, which activated the key ready flag, was improper and flow proceeds to block 216. From block 233, flow proceeds to block 236 if the microcontroller determines that the display is not displaying current-related

information.

At this point, the microcontroller has determined that a switch was

depressed and released (block 218) and that it was not the "function" switch (block 220). Since the only other switch is the "select" switch, the microcontroller deduces that the "select" switch has been depressed and released. The "select" switch is engaged by the user when it is desired to switch to the next of the six submodes of the configuration mode. If the last of the six submodes is displayed when the "select" switch is engaged, a transition to the first submode is displayed. From block 236, flow proceeds to blocks 232 and 214 to change the display.

While the invention has been particularly shown and described with reference to a particular embodiment, various modifications may be made. For example, the microcontroller (or microcomputer) 18 of FIG. la may be implemented using discrete circuits. Further, rather than reactivating power solely by the switch 50 of FIG. la, power may be continuously provided from the battery to a data sensing circuit, such as the interface circuit 16 of FIG. la, so that the data sensing circuit momentarily forward biases the diode 54 to initiate power to the device of FIG. 1. A conventional "one-shot" circuit may "OR"-tied with the switch 50 to couple the data sensing circuit to the diode 54. It will be recognized by those skilled in the art that such modifications and changes may be made to the present invention described above without departing from the spirit and scope thereof.

Claims

What is claimed is:

1. A communication device for communicating with a circuit breaker

trip unit, comprising: a keypad; a display; interface means for coupling data sent from the trip unit with the

communication device; a control circuit, responsive to the keypad and to the data sent from the trip unit, for controlling the display; a local power source which provides power to the communication device; and a power switch, responsive to the control circuit, for disabling the

power pack during periods when data is not being received from the trip unit.

2. A communication device, according to claim 1, wherein the control circuit includes timing means for timing periods during which data is not received from the trip unit.

3. A communication device, according to claim 2, wherein the control circuit sends a signal to the power switch to disable the local power source when the timing means indicates that data has not been received from the trip unit for a prescribed period of time.

4. A communication device, according to claim 1, wherein the keypad includes a plurality of momentary switches.

5. A communication device, according to claim 4, wherein the plurality of momentary switches includes a first switch to select one of a plurality of display modes and a second switch to select one of a plurality of submodes

associated with one of said plurality of display modes.

6. A communication device, according to claim 1, wherein the control circuit includes a microcomputer which receives and interprets the data sent from the trip unit.

7. A communication device, according to claim 6, wherein the microcomputer controls the display by responding to the first and second switches.

8. A communication device, according to claim 1, further including a momentary switch which is used to initiate system power from the local power source.

9. A communication device, according to claim 8, wherein the control circuit includes means, responsive to the initiation of power, for maintaining and controlling the local power source after the momentary switch initiates power.

10. A portable communication device for communicating with a circuit breaker trip unit, comprising: a keypad; a display;

electrically isolated interface means for coupling data sent from the

trip unit with the portable communication device; a microcomputer circuit, which interprets signals received from the

keypad and receives the data sent from the trip unit to control the display, and includes timing means for indicating when data has not been received from the trip unit for a prescribed period of time; a local power source which provides power to the portable communication device independently of power provided to the trip unit;

and a power switch, coupled to the microcomputer circuit, configured to disable the local power source in response to the timing means indicating that data has not been received from the trip unit for the prescribed period of time.

11. A portable communication device, according to claim 10, wherein the electrically isolated interface means includes an optical isolator.

12. A portable communication device, according to claim 10, wherein the microcomputer circuit commands the power switch to shut down the local power source after the prescribed period of time.

13. A portable communication device, according to claim 10, wherein the keypad includes a plurality of momentary switches.

14. A portable communication device, according to claim 13, wherein the plurality of momentary switches includes a first switch to select one of a plurality of display modes and a second switch to select one of a plurality of submodes associated with one of said plurality of display modes.

15. A portable communication device, according to claim 14, further including a third momentary switch which is used to initiate system power from the local power source.

16. A portable communication device, according to claim 14, wherein the plurality of display modes includes a first mode associated with displaying currents monitored by the trip system.

17. A portable communication device, according to claim 14, wherein the microcomputer circuits controls the display by responding to the first

and second switches.

18. A portable communication device, according to claim 10, wherein the microcomputer circuit includes means for maintaining and controlling the local power source.

19. A portable communication device, according to claim 10, wherein the timing means includes an interrupt driven timing program.

20. A portable communication device for communicating with a circuit breaker trip unit, comprising: a manually operable power-up switch for initiating power to the device; a first push-button switch which is engaged to select one of at least two display modes and a second push-button switch which is engaged to select one of at least two display submodes; a display; an optical waveguide for coupling data sent from the trip unit with the portable communication device; a microcomputer circuit, which interprets signals received from the keypad and receives the data sent from the trip unit to control the display,

and including timing means for indicating when data has not been received from the trip unit for a prescribed period of time; a local power source which provides power to the portable

communication device independently of power provided to the trip unit; and a power switch, coupled to the microcomputer circuit, configured to disable the local power source; wherein the microcomputer circuit commands the power switch to disable the local power source in response to the timing means indicating that data has not been received from the trip unit for the prescribed period of time.