United States Patent [191
`Paulsen et al.
`
`[11] Patent Number:
`[45) Date of Patent:
`
`4,853,619
`Aug. 1, 1989
`
`[54] DIGITAL PANEL METER
`[75]
`Inventors: Brian Paulsen, Monument Beach;
`Joseph Vignolo, Dedham, both of
`Mass.
`[73] Assignee: R. T. Engineering Service, Inc.,
`Mansfield, Mass.
`[21] Appl. No.: 156,931
`[22] Filed:
`Feb. 17, 1988
`[51]
`Int. Cl,4 ...................... G01R 19/00; G01R 29/00
`[52) U.S. Cl .................................. 324/115; 324/99 D;
`324/114
`[58] Field of Search ..................... 324/115, 114, 99 D,
`324/123 R, 119; 340/660, 661, 662, 663
`References Cited
`U.S. PATENT DOCUMENTS
`3,979,657 9/1976 Yorksie ........................... 340/661 X
`4,000,463 12/1976 Katzmann eta!. ............. 324/115 X
`4,115,733 9/1978 Silberberg ........................ 324/99 D
`4,157,501 6/1979 Cain, Jr. et al .......... ., ..... 324/115 X
`4,251,769 2!1981 Ewert et al ..................... 340/661 X
`4,321,530 3/1982 Kelly et a!. ..................... 324/115 X
`4,422,039 12/1983 Davis .............................. 324/119 X
`4,641,090 2/1987 Danby ............................. 324/115 X
`
`[56)
`
`4,748,404 5/1988 Heinze eta!. ................... 324/115 X
`
`FOREIGN PATENT DOCUMENTS
`2055480 3/1981 United Kingdom ................ 324/115
`
`OTHER PUBLICATIONS
`"New Concept Hioki Digital Multimeters:'; Cat No.
`3207 E; 1980; pp. 1-4.
`Primary Examiner-Reinhard J. Eisenzopf
`Assistant Examiner-Vinh P. Nguyen
`Attorney, Agent, or Firm-Wolf, Greenfield & Sacks
`[57]
`ABSTRACf
`A digital panel meter adapted for replacement of a
`standard analog panel meter and designed to selectively
`receive different ranges of input signals such as AC or
`DC input signals. The meter circuitry employs an ana(cid:173)
`log-to-digital converter having multiple digits, an input
`circuit including a range circuit, an operational ampli(cid:173)
`fier and filter circuitry. A relay is tripped for signaling
`the attaining of a trip point. An audible alarm is pro(cid:173)
`vided that may be enabled or disabled and that may be
`operated in either continuous or short term modes.
`
`15 Claims, 6 Drawing Sheets
`
`TO PROGRAM TRIP POINT
`USE SWITCH POSITIONS 1 AND 2
`
`RUN MODE
`
`TRIP POINT SET MODE
`
`TO PROGRAM AUDIBLE ALARM
`USE SWITCH POSITIONS 3 AND 4
`,.:?------,
`CONTINUOUS AUDIBLE ALARM
`AT AND ABOVE TRIP POINT
`
`30 SECOND AUDIBLE ALARM
`AT AND ABOVE TRIP POINT
`
`"SILENCE"
`NO AUDIBLE ALARM
`
`IPR Page 1
`
`Raritan v. Server Technology
`
`RARITAN EXHIBIT 1025
`
`

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`IPR Page 2
`
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`IPR Page 3
`
`

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`
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`
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`
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`
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`
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`P5
`
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`
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`Cl2
`
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`
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`
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`
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`Rl6
`
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`
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`
`FIG.1D
`FROM R9
`
`-------------------
`
`I
`FROM FIG. 1A >------,
`
`----
`
`lOOK
`R26
`
`DB
`
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`j
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`
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`
`IPR Page 4
`
`

`
`U.S. Patent
`
`Aug. 1~ 1989
`
`Sheet 4 of 6
`
`4,853,619
`
`FROM {
`FIG.18
`
`.....
`
`~------k--r-----
`\
`
`t5V
`SOURCE
`
`I
`
`13
`
`~ R13
`Rl2
`>330 1330
`
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`
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`
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`4
`OS-I
`MAN6630
`
`I
`
`---------
`+5V
`SOURCE
`
`~ Rl4
`~ 330
`
`4
`
`DS-2
`MAN6610
`
`I
`13
`
`14
`
`' I
`
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`
`J
`
`I 2 3 5 6 7 8 10 II 12 15 16 17 18
`
`20 19 18 15 22 24 16 23 17
`
`~
`
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`
`14 9 10 8 2 7 3 4 5 6 II 12 25 13
`IC-2
`ICL7107CPL
`31 32 33 34 353638
`~-
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`
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`
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`
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`
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`
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`
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`
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`TO
`REF. 5
`FIG.1C
`
`FIG.!D
`
`39
`
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`lOOK +1.2 v
`SOUR CE
`/30
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`25T
`
`IPR Page 5
`
`

`
`U.S. Patent
`
`Aug. 1,1989
`
`Sheet 5 of 6
`
`4,853,619
`
`/6
`
`10
`
`12
`
`iBB
`
`SW1
`
`22 ol
`
`0000
`000
`0000
`0
`
`TO PROGRAM TRIP POINT
`
`USE SWITCH POSITIONS 1 AND 2
`
`SW1
`
`RUN MODE
`
`i O O§l ~ TRIP POINT SET MODE
`oN~~nn
`
`I 2 3 4
`
`SW1
`
`TO PROGRAM AUDIBLE ALARM
`USE SWITCH POSITIONS 3 AND 4
`ON~ ~ ~ Ej
`r 1 2 3 4
`
`CONTINUOUS AUDIBLE ALARM
`AT AND ABOVE TRIP POINT
`
`SW1
`
`ON 0 n n ~ 30 SECOND AUDIBLE ALARM
`i ~ ~ ~ 0
`1 2 3 4
`
`AT AND ABOVE TRIP POINT
`
`SW1
`
`oNnnnn
`i 1 2 3 4
`~~~~
`
`"SILENCE"
`NO AUDIBLE ALARM
`
`FIG2
`
`IPR Page 6
`
`

`
`U.S. Patent Aug. 1, 1989
`
`Sheet 6 of 6
`
`4,853,619
`
`14
`
`0
`
`0
`
`10
`
`0
`
`34
`
`F!G.3
`
`0
`
`IPR Page 7
`
`

`
`1
`
`DIGITAL PANEL METER
`
`4,853,619
`
`2
`that can be used with utilization apparatus. The meter
`circuitry also includes an audible alarm. The audible
`alarm is controlled from a switch means that may be
`used to either enable o disable the audible alarm. There
`is also provided a second switch means for selecting
`different modes of operation including a continuous
`mode and a short term mode. Both of these switch
`means are operable by the meter user. A plurality of
`operating switches are also provided associated with
`the input terminal means and for enabling selection of a
`decimal point position.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`Numerous other objects, features and advantages of
`the invention should now become apparent on a reading
`of the following detailed description taken in conjunc(cid:173)
`tion with the accompanying drawings, in which:
`FIGS. 1A-1D illustrate an overall circuit diagram for
`the meter circuitry of the present invention;
`FIG. 2 is the front view of the digital panel meter of
`this invention; and
`FIG. 3 is a rear elevation view of the meter illustrated
`if FIG. 2.
`
`10
`
`BACKGROUND OF THE INVENTION
`The present invention relates in general to meters and 5
`it is concerned, more particularly, with a digital panel
`meter that is primarily adapted as a replacement meter
`for a standard analog panel meter. Even more particu(cid:173)
`larly, the present invention relates to a digital panel
`meter having an associated alarm relay.
`Reference is now made to U.S. Pat No. 4,157,501 on
`a digital panel meter owned by the present assignee
`herein. This prior patent describes. a digital panel meter
`including an input range circuit employing jumpers for
`selecting different amplitude ranges. Although the digi- 15
`tal panel meter described in this patent is more than
`adequate for its intended usage, it does not provide any
`external signaling upon attaining a trip point.
`Accordingly, it is an object of the present invention
`to provide an improved digital panel meter and one 20
`which in particular has means for providing an output
`signal indicating the attaining of a particular trip point
`usually set by .the user of the meter.
`A further object of the present invention is to provide
`a digital panel meter that is easy to install and calibrate 25
`even by a non-technical person.
`Another object of the present invention is to provide
`a digital panel meter that is relatively compact and that
`permits a decimal point setting by switch means.
`Another object of the present invention is to provide 30
`an improved digital panel meter that has an audio signal
`circuit for providing an audio signal in response to at(cid:173)
`taining the trip point.
`Another object of the present invention is to provide
`an improved digital panel meter as in accordance with 35
`the preceeding object and in which the audio signal may
`be enabled or inhibited, and in which the audio signal
`may also be selected to be of continuing or short dura(cid:173)
`tion.
`
`40
`
`SUMMARY OF THE INVENTION
`To accomplish the foregoing and other object, fea(cid:173)
`tures and advantages of the present invention, there is
`provided a digital panel meter which is comprised of a
`housing for mounting the majority of components com- 45
`prising the meter circuitry. Preferably, a terminal strip
`is mounted at the rear of the housing including input
`terminal means for receiving signals to be measured.
`The circuitry of the panel meter of this invention in(cid:173)
`cludes a range circuit that preferably has a jumper
`means for selecting one of a plurality of different ampli(cid:173)
`tude ranges. The jumper means is easily accessible at the
`rear of the meter being connectible between different
`terminals on the terminal strip. Another connection to
`the terminal strip is an input AC power connection
`which couples to a power supply for the meter which
`provides a regulated output voltage. The meter cir(cid:173)
`cuitry also comprises amplifier means, filter means and
`an analog to-digital converter means. The amplifier
`means is preferably an operational amplifier having an 60
`input coupling from the range circuitry and having its
`output coupled by way of filter means to the analog-to(cid:173)
`digital converter.
`In accordance with the invention, the meter circuitry
`also includes a comparator having a preset input, that is 65
`preset by the meter user. This may be preset at a partic(cid:173)
`ular trip point. The output of the comparator couples to
`a relay for providing an output signal from the meter
`
`DETAILED DESCRIPTION
`FIGS. 1A-1D illustrate a schemetic diagram of the
`meter's circuity.
`· FIG. 2 illustrates a front view of the meter and FIG.
`3 a rear view of the meter.
`As illustrated in FIG. 2, the meter comprises a hous(cid:173)
`ing 10 which may be constructed of either steel or a
`plastic material and which may be provided in two
`separate parts. In the front view of FIG. 2 there is
`shown the display 12 which is a four digit display view(cid:173)
`able at the front of the housing 10. The housing 10 may
`also have therein a printed circuit board or the like for
`mounting electronic components such as at least some
`of the components shown in FIGS. 1A-1D.
`The meter of this invention may be inserted in a panel
`such as an instrument control panel and for the purpose
`of mounting the meter there is provide series of mount(cid:173)
`ing screws that may be disposed at each comer of the
`housing. FIG. 3 shows at the comers of the housing the
`holes for the mounting screws.
`In connection with FIG. 2 and the front of the meter,
`in addition to the display at 12, there is also provide a .
`trip point and audible alarm programming switch SW1,
`a zero set adjust 16, a trip point adjust 18, a flashing
`so LED indicator 20, and porting means 22 for the audible
`alarm. Many of the items illustrated in FIG. 2 will be
`refered to hereinafter in connection with the description
`of the meter circuitry in FIGS. 1A-1D. FIG. 2 also
`illustrates the different settings for the switch array of
`55 switch SW1 for both programming the trip point as well
`• as programming of the audible alarm type.
`FIG. 3 shows the rear of the meter housing including
`the terminal strip 14 compised of a series of electrically
`isolated terminals 15. The input AC power is coupled at
`input AC terminals 25. The input signal to be measured
`is coupled at the input terminals 27. The terminals illus-
`trated at 28 are for accommodating a scaling jumper
`with four separate possible positions as illustrated in
`FIG. 3 by respective positions A, B, C and D. These
`relate to corresponding similar positions illustrated in
`the meter circuitry to be described hereinafter.
`FIG. 3 also illustrates a calibration potentiometer 30
`and the decimal point placement switch 32. Disposed
`
`IPR Page 8
`
`

`
`4,853,619
`
`3
`under the terminal strip 14 are the solid state switching
`terminals 34. These terminals may be connected to some
`type of a utilization device that senses the state of the
`meter. Generally speaking, there is either a short across
`these terminals to signal an external device that a trip 5
`point has been reached. When there is an open across
`these terminals this indicates that the trip point has not
`yet been reached. Further discussion follows regarding
`the items in FIG. 3 in connection with the circuit dia(cid:173)
`gram of FIGS. 1A-1D.
`The panel meter of this invention is a versatile instru(cid:173)
`ment and is designed to fit in the same mounting cutouts
`as a standard 4! inch analog meter, yet it will accept a
`wide range of voltage inputs from a wide variety of
`input signal devices. The unit can be very simply cali- 15
`brated via a 25 tum potentiometer at the rear of the
`housing, namely potentiometer 30 illustrated in FIG. 3.
`Basically, the meter can be calibrated to read any 3~
`
`4
`internal relay for providing, for example, an alarm to a
`user when a measured parameter exceeds a predeter(cid:173)
`mined value. This relay is illustrated in the meter cir-
`cuitry as relay K1 having associated contacts illustrated
`at K1A. The level at which the relay contacts are set to
`close, is easily set via a ten tum potentiometer disposed
`underneath the display. This is the potentiometer 18 in
`Fig. 2. Once set the relay contact will close when the
`display value becomes greater than or equal to the value
`10 which was set. A LED 20 blinks on and off and is visi(cid:173)
`ble through the display bezel. If desired, an audible
`alarm can be made to sound when the contacts become
`closed. A further option is that the audible alarm can be
`made to silence itself after 30 seconds or can be continu(cid:173)
`ous. This is controlled from various contacts of the
`switch array SW1.
`The following is a listing of certain specifications
`pertaining to the meter.
`
`Input Ranges
`
`Maximum Input & Overvoltage
`
`Accuracy
`Input Resistance at Nominal
`Scale Values
`A.C. Voltage Measurements
`Maximum Signal Frequency
`Minimum Input Frequency
`
`Sampling Time
`Response (000 to 1999)
`Relay Contacts
`Type
`Rating
`Trip Level Repeatability
`Power Requirement
`
`Operating Temperature
`Typical Signal Inputs
`
`Display
`
`Overrange
`
`Weight
`
`(A) 50 Millivolts DC (100 Millivolts AC)
`(B) 5 VDC (10 VA C)
`(C) 50 VDC (100 VAC)
`(D) 500 VDC (480 VAC)
`1000% of range or 500 VDC (480 VAC)
`whichever is less
`0.5% linear +I digit F.S.
`20K Ohms/Volt D.C.
`9K Ohms/Volt A.C.
`
`2KHz
`40Hz - extends down to l Hz for
`readings of 010 or below (A. C.
`Tachometers
`3 Readings/Second Update
`6.5 Seconds
`
`Internally Fused N.O. Solid State Triac
`IISV AC 50/60Hz, .5 Amps (500 Milliamps)
`0.1% of Full Scale (±I Digit)
`115V AC Nominal ( + IOV), 50/60Hz, 2
`Watts, (230VAC, 50/60 Hz Optional)
`5 c. to soc.
`A.C. or D.C. Signals from : Line
`Voltage, Reference Voltage
`Tachometers, Force Transducers (Load
`Cells), Shunt, Current Transformers,
`Pressure & Flow Transducers
`3~ Active Digit (0-1999). 0.5 Inch
`LED Non-blinking. Optional decimal
`points at the following positions:
`1.8.8.8 (user selectable)
`Indication by a"!" in the most
`significant position with remaining
`display unlit.
`I Pound
`
`digit parameter required from 0.000 to 1999 with user
`selectable decimal points at three locations. In this re(cid:173)
`gard note the decimal point switch 32.
`With regard to the switch 32 it is noted that in past
`units it has been typical to provide jumpers for decimal 55
`point selection. However, with meter circuitry of the
`type described herein, it is common to have some rela(cid:173)
`tively large voltages that may be present. In this regard
`it is noted that in the meter circuitry the switch 32
`couples to the primary of transformer Tl and it has been 60
`found that there are common mode voltages that can
`present some danger in connection with the use of
`jumpers for decimal point selection. Accordingly, in
`accordance with the present invention a decimal point
`selection switch has been used as illustrated.
`The meter of the present invention differs in a number
`of ways from the digital meter described in U.S. Pat.
`No. 4,157,501. For one thing, this meter now has an
`
`65
`
`As indicated above, the meter of this invention can
`accept either AC or DC input signals at the terminals
`27. These signals are coupled by way of a scaling
`(range) network 40 and a variable gain half-wave recti(cid:173)
`fier circuit 42. The inputs at the terminals 27 and 28 may
`be either AC or DC or a constant area pulse train with
`ranges as previously indicated. The input impedances
`for each range are represented by the resistors R1-R4 of
`respective values 10 meg ohms, 1 meg ohm, 100 k ohm
`and 1 k ohm. Of course only one of the resistors R1-R4
`are selected at a time by. means of the jumper Jl, to
`couple the input signal to input 43 of the operational
`amplifier 44.
`The operational amplifier 44 is preferably a conven(cid:173)
`tional operational amplifier as a type LM 741 having an
`offset null controlled by potentiometer 16, a pair of
`input terminals at 43, and an output terminal 46. Also
`
`IPR Page 9
`
`

`
`4,853,619
`
`55
`
`5
`illustrated in this circuitry are a pair of oppositely ar(cid:173)
`ranged diodes D1 and D2 which limit the voltage dif(cid:173)
`ference at the input terminals of the amplifier, both in a
`positive and negative sense. The diode D3, which is
`coupled across the operational amplifier 44 is prevent- 5
`ing excessive slew times and AC non-linearities by limit(cid:173)
`ing the negative output of the amplifier 44 to about
`-0.6 volts which occurs during the negative half cycles
`when considering AC operation.
`For AC or pulsed modes of operation the output at 10
`the cathode of diode D4 is a half-wave rectified signal
`having the usual sinusoidal positive portion of the signal
`and a clipped negative portion which is clipped at ap(cid:173)
`proximately 0.6 volts. Thus, the operational amplifier 44
`actually forms an inversion with any negative signals at 15
`its input appearing as ~positive voltage level at the
`output of the amplifier.
`·
`The output from the rectifier couples to a filter circuit
`which is preferably a compound smoothing filter com(cid:173)
`prised of resistors R5-R7 along with capacitors C5 and 20
`C6 connected as a ladder network. In one embodiment
`the roll-off of this filter may be approximately
`40dB/ decade above 0. 7 Hz.
`The output signal from the filter couples by way of
`line 48 to the input of the analog-to-digital converter 49. 25
`The signal along line 48 also couples to the comparator
`50. The analog-to-digital converter 49 may be of type
`ICL 7107 CPL. The comparator 50 may be of the type
`IC 4 A. Associated with analog-to-digital converter 49
`are the display devices 12. This provides the display as 30
`illustrated in FIG. 2. The display devices may be of type
`MAN 663 and MAN 6610 as illustrated. It is also noted
`that the three separate decimal point select switches of
`switch array 32 couple to appropriate inputs of the
`display 12 so as to provide proper decimal point selec- 35
`tion, as desired by the user.
`Thus, the basic input signal couples to one of the
`inputs of comparator 50 while the other input of the
`comparator at line 51 is a reference input. This is cou(cid:173)
`pled from operational amplifier 52 which in tum is 40
`adjusted by means of the trip-point adjustment potenti(cid:173)
`ometer 18. There is also a second factory set potentiom(cid:173)
`eter 54 illustrated in the meter circuitry and this also
`couples to the input line 51 of the comparator 50. It is
`also noted that at the input to the comparator 50 there 45
`is provided the switch contact SW1-2. In its open posi(cid:173)
`tion the contact SW1-2 has no effect on the circuit but
`when it is closed this switch contact couples with the
`trip-point adjustment circuitry directly to the display
`for setting the trip-point level. This would be in the 50
`trip-point set mode as illustrated in FIG. 2. In that mode
`the switch contact SW1-2 is also closed to prevent the
`relay K1 from triggering by essentially grounding both
`sides of the relay. Note that one side of contact of
`SW1-1 is coupled to ground.
`When the comparator 50 is at its non tripped state, the
`output therefrom is at a more negative voltage level
`maintaining the transistor Q1 non-conductive. When
`the comparator 50 does trip then the transistor Q1 con(cid:173)
`ducts and energizes the relay K1 through the resistor 60
`R15. When the transistor Q1 conducts this also ener(cid:173)
`gizes the flashing LED 20 by way of the Zener diode
`D8. When the relay K1 energizes the associated contact
`K1A is energized to provide an indication at the output
`terminals 34 usable at another utilization device as de- 65
`termined by the user of the product.
`When the relay K1 energizes, there is also a driving
`voltage coupled by wa of the resistor R22 to the piezo-
`
`6
`buzzer 60 to provide an alarm. Associated with the
`buzzer 60 is an oscillating transistor Q2, diode Dll and
`associated resistor R20 and R21. The piezo-buzzer 60 is
`arranged to provide a continuous audible signal under
`control of the oscillating transistor Q2. The transistor
`Q2 is enabled from the output of the operational ampli(cid:173)
`fier 62. The circuitry also depicts the switch contact
`SW1-4 which is a tone enable contact. In its open posi(cid:173)
`tion there is no signal coupled to the transistor Q2 and
`thus the audible tone is disabled. This is also illustrated
`in FIG. 2 as a "silence condition". The operational
`amplifier 62 is operated by way of diode 6 and resistor
`R25 essentially from the output of comparator 50.
`There is also provided in the circuitry the other switch
`contact SW1-3 that controls whether the audible tone is
`to be continuous or only over some previously deter(cid:173)
`mined interval set up in this circuit as being for a thirty
`second interval. If the switch is closed then the capaci(cid:173)
`tor C12 is essentially short circuited and this would be
`for a continuous tone. When the switch SW1-3 is
`opened then a charging of the capacitor C12 occurs and
`there is a time-out for controlling the enable signal
`coupled to the transistor Q2.
`As far as the AC input is concerned at terminals 25,
`this is a conventional AC input voltage coupled by the
`way of fuse F1 to the primary winding P of transformer
`T1. The secondary winding S of transformer T1 has a
`grounded center tap and has its other two connections
`coupled to a full wave rectifier bridge 70. There are a
`pair of capacitors C1 and C2 associated with the output
`of the bridge circuit 70. The voltage across these capac(cid:173)
`itors is an unregulated voltage that can be used, for
`example, for the operational amplifier 44. The output of
`the bridge circuit 70 also couples to regulators VR1 and
`VR2. On one side the circuit includes capacitor C3,
`resistor R10 and Zener diode VR3. On the other side
`there is simply the compacitor C4. These provide re(cid:173)
`spective voltages plus 1.2 volts and -5 vvlts. These
`voltages may be used for example, at the analog-to-digi(cid:173)
`tal converter 49.
`In using the meter of this invention the standard 115
`AC is coupled at the terminals 25. The meter is inter(cid:173)
`nally fused as indicated. The signal terminals are con(cid:173)
`nected to the input terminals at 27. If the signal is a DC
`signal, the polarity should be correct. Low voltage
`signals, or signals relating to a reference or feedback for
`a device system are to be run in a shielded cable to
`minimize any noise pickup from the cable run. The
`shield should be connected to the meter common. The
`other end of the shield is to remain unconnected and
`insulated using electrical tape.
`As far as the range circuit is concerned, if the maxi(cid:173)
`mum voltage of the signal is not known, one can fasten
`the jumper J1 to the highest range, namely terminal D.
`One then applies the maximum signal and adjusts the
`"read-out scale" adjustment 30 at the rear of the meter,
`until the desiretl display reading is obtained. If the meter
`display cannot be adjusted to read high enough, the
`signal input is removed. The jumper is then unfastened
`and placed on the lower range namely terminal C. The
`signal is reapplied and again the adjustment is made to
`obtain the desired display reading. This continues until
`the proper range has been obtained.
`As far as setting the meter relay is concerned, this
`adjustment is made only after the meter has been cali(cid:173)
`brated. The switch contacts SW1 and SW2 are moved
`to their "on" position. A trip light comes on. Using a
`small screwdriver one can make an adjustment until the
`
`IPR Page 10
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`

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`4,853,619
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`25
`
`8
`7
`4. A digital panel meter as set forth in claim 3 wherein
`display reads the number desired for tripping the meter.
`said means for selecting includes a jumper selectively
`The switch contacts SW1 and SW2 are then moved to
`coupled to only one of said scaling resistors.
`their "off'' position or "open" position. The meter is
`5. A digital panel meter as set forth in claim 4 includ-
`now ready to operate.
`When the display reads the number or higher than the 5
`ing a pair of oppositely poled diodes across the input of
`the operational amplifier.
`number set, the relay contacts close. The red trip light
`goes on and blinks, this is the LED 20, to show that the
`6. A digital panel meter as set forth in claim 5 wherein
`~::!v~!~~r means includes a resistor-capacitor ladder
`meter has tripped. The contacts remain closed until the
`display value again becomes less than the number set. 10
`7. A digital panel meter as set forth in claim 6 includ-
`As far as the audible alarm is concerned, if the switch
`ing a scale potentiometer across the operational ampli·
`tier for calibration purposes of the display.
`contact SW1-4 is on an audible alarm sounds as the
`meter goes above the set or trip point. If the switch
`8. A digital panel meter as set forth in claim 1 includ-
`ing a diode connected between the input and output of
`contact SW1-3 is on the alarm remains on as long as the
`meter stays above the set point. However if the switch 15 the amplifier means.
`9. A digital panel meter as set forth in claim 1 wherein
`contact SW1-3 is off then the meter automatically si-
`lences itself after 30 seconds.
`said range circuit means include a plurality of different
`Having now described a limited number of embodi-
`value scaling resistors, said means for selecting includ-
`ments of the present invention, it should now be appar-
`ing a jumper selectively coupled to one of said scaling
`ent to those skilled in the art that numerous other em- 20 resistors, said terminal strip including terminals for said
`bodiments and modifications thereof are contemplated
`jumper.
`10. A digital panel meter as set forth in claim 1 includ-
`as falling within the scope of the present as defined by
`the appended claims.
`ing means for providing an audible alarm in response to
`What is claimed is:
`the setting of said relay.
`1. A digital panel meter comprising;
`11. A digital panel meter as set forth in claim 10 in-
`a housing,
`eluding first switch means for enabling said audible
`input terminals means for receiving AC and DC input
`alarm.
`12. A digital panel meter as set forth in claim 11 in-
`signals,
`range circuit means including means responsive to
`eluding a second switch means for selecting between
`30 either continuous alarm or an alarm of predetermined
`the output of the input terminal means and means
`short duration.
`for selecting one of a plurality of different ampli-
`13. A digital panel meter as set forth in claim 1 includ-
`tude ranges,
`ing a first switch associated with said comparator means
`amplifier means responsive to the output of the range
`and means for adjusting the trip-point, said switch pro-
`circuit means and having an output,
`35 viding for direct coupling of the set-point adjustment to
`a rectifier means responsive to the output of the am-
`the display means.
`plifier means,
`14. A digital panel meter as set forth in claim 13 in-
`filter means responsive to the output of the rectifier
`eluding a second switch far disabling the relay when the
`means,
`first switch is used to set the trip-point.
`analog-to-digital converter means responsive to the 40
`15. A digital panel meter comprising:
`filter means,
`a housing;
`display means mounted in the housing and coupled
`a terminal strip associated with the housing and in-
`from said analog-to-digital converter means,
`eluding input terminal means;
`a terminal strip at the rear of the housing including
`range circuit means including means coupled from
`terminals forming the input terminal means and AC 45
`the input terminal means and means for selecting
`power terminals,
`one of a plurality of different amplitude ranges;
`a comparator means responsive to the output of the
`detection circuit means including amplifier means
`ftlter means, means for establishing an adjustable
`coupled from said range circuit means and having a
`reference input to the comparator means for estab-
`detection circuit means output;
`lishing a trip-point,
`analog-to-digital converter means coupled from said
`relay means coupled from the output of said compar-
`detection circuit means;
`difr~~ ::::~~:-~~:~i~~t:f~o~~~~~~ ~~~n~~upled
`ator means and adapted to be set when the compar-
`ator means triggers, and
`_a comparator means responsive to the output of said
`a plurality of separately operable decimal point set- 55
`detection circuit means, and means for establishing
`ting switches coupled to said display means for
`an adjustable reference input to the comparator
`manual setting of the decimal point in the display
`means for establishing a trip-point;
`means.
`means coupled from the output of said comparator
`2. A digital panel meter as set forth is claim 1 wherein
`means and adapted to be set when the comparator
`said amplifier means includes an operational amplifier 60
`means triggers;
`·
`and said rectifier means includes a diode.
`decimal point setting switch means coupled to said
`3. A digital panel meter as set forth in claim 2 wherein
`display means and including means for manually
`said range circuit means includes a plurality of different
`setting one of a plurality of different settings of the
`value scaling resistors each coupling to a signal input of
`decimal point in the display means.
`* * * * *
`the operational amplifier.
`
`50
`
`65
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`IPR Page 11