Low voltage indicator

Claim 2

In association with an electric distribution system, apparatus for monitoring and registering for subsequent interrogation an occurrence at monitoring terminals, sustained for at least a predetermined time period, of a system voltage less than a predetermined voltage, comprising: a. threshold voltage sensing means adapted to be connected to said monitoring terminals and having an output switchably responsive to said system voltage dropping below said threshold voltage; b. timing and lockout means connected to said threshold voltage sensing means and having a two-state switchable output for timing said predetermined time period and locking into and maintaining one of the two states when said system voltage is sustained below said threshold voltage for a period in excess of said predetermined time period, and having first and second switches, the output of each of said switches being connected to the input of the other switch so that when one of said switches is closed the other of said switches is open; and c. readout means coupled to said two-state switchable output for reading out the state of said timing and lockout means to determine whether said system voltage had been continuously below said predetermined voltage for a period in excess of said predetermined time period.

Claim 3

The apparatus as described in claim 1, wherein said threshold sensing means comprises: a. a voltage divider; b. a zener diode connected to the output of said voltage divider; c. a rectifier connected in series with said zener diode to rectify current through said zener diode; and d. threshold switching means connected to and driven by said rectifier, for providing a switchable two-state high-low conductance path between said threshold voltage sensing means output and one of said monitoring terminals.

Claim 4

The apparatus as described in claim 2 wherein said voltage divider contains a temperature responsive element for compensating for variations in the operating characteristics of said zener diode with respect to temperature.

Claim 5

The apparatus as described in claim 2, wherein said threshold switching means comprises a Darlington transistor having its base resistively connected to said rectifier, its emitter connected to said one of said monitoring terminals, and its collector being the threshold voltage sensing means output.

Claim 6

The apparatus as described in claim 1, wherein said timing and lockout means comprises: a. voltage divider means for dividing said monitored system voltage, connected to said monitoring terminals; b. rectifier supply means connected to the output of said voltage divider means for providing a rectified voltage; c. timing means actuated from the output of said threshold voltage sensing means for timing out when said system voltage has continuously remained below said threshold voltage for at least said predetermined period, said timing means being connected to said rectifier supply means; and, d. said timing means including timing switch means for actuating said two-state switchable output.

Claim 7

The apparatus described in claim 5, wherein after said timing means begins to time out following an occurrence of a drop in said system voltage below said threshold voltage but before timing out, said system voltage rises above said threshold voltage, said timing means is restored to its condition previous to beginning of timing out, in preparation for again beginning to time out on a subsequent occurrence of said system voltage dropping below said threshold voltage.

Claim 8

The apparatus as described in claim 5, comprising arming means for arming said timing means for subsequent threshold sensing.

Claim 9

The apparatus as described in claim 5, wherein said timing means comprises a timing capacitor in series with a resistor, said timing capacitor and resistor being in series with a timing switch which provides a discharge path for said timing capacitor.

Claim 10

The apparatus as described in claim 8 wherein said resistor and said timing capacitor have a time constant such that, when said timing capacitor discharges through said timing switch, the current supplied to said timing switch from said timing capacitor falls to a level at which said timing switch is turned off in said predetermined time period.

Claim 11

The apparatus as described in claim 5 wherein said timing switch means comprises a transistor switch with its input connected to said rectifier supply means through a blocking diode and said timing means and said blocking diode cooperate to switch off said transistor switch upon the occurrence of said threshold switching means switching to a low conductance path.

Claim 12

The apparatus as described in claim 1, wherein said readout means comprises: a. voltage divider means connected to said monitoring terminals for providing a fraction of said monitored voltage; b. readout display means, for providing a readout signal indicative of the state of the switchable output of said timing and lockout means; c. coupling means for coupling said output of said timing and lockout means to said readout display means; and, d. interrogating means, for interrogating said readout display means.

Claim 13

The apparatus as described in claim 11, wherein said readout display means comprises a silicon controlled rectifier in series with a display element, said coupling means comprises a second voltage divider having an output connected to the gate of said SCR, and said interrogating means comprises a switch in series with said display element.

Claim 14

The apparatus as described in claim 11, wherein said interrogating means comprises remotely controlled interrogating switch means.

Claim 15

The apparatus as described in claim 1, in combination with a watthour meter driven by and connected to said monitored system voltage, said threshold voltage sensing means, said timing and lockout means, and said readout means being fixed within the housing of said watthour meter.

Claim 16

Apparatus as described in claim 1 wherein said timing and lockout means comprises: a. a voltage divider; b. a rectifier connected to the output of said voltage divider, to provide a normal rectified voltage; and, c. timing means connected to said rectifier for timing out when said system voltage has continuously remained below said threshold voltage for at least said predetermined period.

Claim 17

Apparatus as described in claim 15 wherein said timing means has a silicon controlled rectifier switch in series with a timing and storage capacitor and a resistor, such capacitor and resistor having a time constant such that said capacitor, when charged to said normal rectified voltage and said threshold switching means is switched to a low conductance state, discharges through said silicon controlled rectifier with the discharge current falling to the level of the holding current of Said silicon controlled rectifier in said predetermined time period.

Claim 18

Apparatus as described in claim 16 comprising arming means for arming said timing means for subsequent threshold sensing.

Claim 19

The apparatus as described in claim 15 wherein said arming means switchably connects said rectifier to the gate of said silicon controlled rectifier to trigger said silicon controlled rectifier.

Claim 20

The apparatus as described in claim 1 comprising zero voltage detection means connected between said sensing means and said timing and lockout means, for maintaining said sensing means unresponsive to a zero system voltage, such that said timing and lockout means is prevented from locking into said one of two states when said system voltage is zero.

Claim 21

The apparatus as described in claim 19, wherein said timing and lockout means comprises a non-interruptable power source, coupling means coupling said non-interruptable source to said sensing means, and voltage-sensitive shunt means in shunt connection with said coupling means, said shunt means being adapted to prevent said sensing means from being switchably responsive to a monitored zero system voltage.

Claim 22

In association with an electric distribution system, apparatus for monitoring and registering for subsequent interrogation an occurrence at monitoring terminals, sustained for at least a predetermined time period, of a non-zero system voltage less than a predetermined threshold voltage, comprising: a. threshold voltage sensing means adapted to be connected to said monitoring terminals and having an output switchably responsive to said non-zero system voltage dropping below said threshold voltage; b. timing and lockout means connected to said sensing means and having a two-state switchable output for timing said predetermined time period and locking into and maintaining one of the two states when said non-zero system voltage is sustained below said threshold voltage for a period in excess of said predetermined time period; c. zero voltage detection means connected between said sensing means and said timing and lockout means, for maintaining said sensing means output unresponsive to a zero system voltage but permitting said sensing means to be responsive to a non-zero voltage less than said threshold voltage; and d. readout means coupled to said two-state switchable output for reading out the state of said timing and lockout means to determine whether said system voltage had been continuously below said predetermined voltage for a period in excess of said predetermined time period.

Claim 23

In association with an electric distribution system, apparatus for monitoring and registering for subsequent interrogation an occurrence at monitoring terminals, sustained for at least a predetermined time period, of a non-zero system voltage less than a predetermined threshold voltage, comprising: a. threshold voltage sensing means adapted to be connected to said monitoring terminals and having an output switchably responsive to said non-zero system voltage dropping below said threshold voltage; b. timing and lockout means connected to said sensing means and having a two-state switchable output for timing said predetermined time period and locking into and maintaining one of the two states when said non-zero system voltage is sustained below said threshold voltage for a period in excess of said predetermined time period; c. zero voltage detection means connected between said sensing means and said timing and lockout means, for maintaining said sensing means output unresponsive to a zero system voltage but permitting said sensing means to be responsive to a non-zero voltage less than said threshold voltage; and d. readout means coupled to said two-state switchable output for reading out the state of said timing and lockout means to determine whether said system voltage had been continuously below said predetermined voltage for a period in excess of said predetermined time period.

Claim 24

The apparatus as described in claim 21 wherein said zero voltage detection comprises a non-interruptable power source, coupling means coupling said non-interruptable source to said sensing means, and voltage-sensitive shunt means in shunt connection with said coupling means, said shunt means being adapted to prevent said sensing means from being switchably responsive to a monitored zero system voltage.