Voltage and continuity checker

• US 4,027,236 A
• Filed: 07/14/1976
• Issued: 05/31/1977
• Est. Priority Date: 07/14/1976
• Status: Expired due to Term

• Current Assignee: Triple S Products Company
• Original Assignee: Triple S Products Company
• Inventors: Stewart, Phillip M.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US05/705,270
• Time in Patent Office: 321 Days
• Field of Search: 324/51, 324/72.5, 324/133, 324/149, 324/53
• US Class Current: 324/556
• CPC Class Codes: G01R 19/145 Indicating the presence of current or voltage
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• CPC Class Codes: G01R 31/54 Testing for continuity

Abstract

A portable test instrument for testing electrical continuity, and diode polarity, AC and DC voltage amplitudes and DC voltage polarity. An electronic switch device has main electrodes connected in an indicating circuit with an electrical supply, a light-emitting diode and a current-limiting resistor. A double pole, double throw switch is manually switchable between continuity and voltage test positions, and with four resistors defines an input circuit interposed between the control electrode of the electronic switch device and probes connectible to a circuit or the like to be tested. In both the voltage and continuity test modes of the instrument, the light-emitting diode is energized only by current from the electrical supply within the indicating circuit. Though proper circuit operation is obtained by manual manipulation of the mode switch between its voltage and continuity positions, the light-emitting diode is automatically protected from damage should the test probes engage a voltage circuit (within the operating voltage range of the instrument) while the instrument is in continuity mode.

Claims

1. A portable instrument for testing electrical continuity, voltage and polarity, comprising in combination:

electronic switch means having main current electrodes and a control electrode actuable for contolling current flow through said main electrodes;

an electrical supply, an indicator and current limiting means connected in series loop with said main current electrodes, wherein current flow through said main current electrodes controls actuation of said indicating means in both the voltage and continuity test modes of the test instrument;

a pair of test probes;

an input impedance network comprising first, second and third impedances in series from one said test probe to said control electrode, respectively, wherein the junction point of said second and third impedances connects to one of said main electrodes such that said third impedance connects across the control electrode and said one main electrode of said electronic switch means, said impedance network further including a fourth impedance connectible between the other test probe and said control electrode only in the voltage test mode of said instrument;

switch means including voltage test terminal means selectable for connectively shunting said second impedance and for establishing said connection of said other test probe with said control electrode through said fourth impedance, said switch means also including continuity test terminal means selectable for conductively connecting said other test probe to said current limiting means and electrical supply of said series loop and for conductively joining the juncture of said first and second impedances with the juncture of said third impedance and control electrode whereby the series loop comprising the main electrodes of said electronic switch means, said electrical supply of said instrument, said indicator means and said current limiting resistor provides the sole current supply loop for said indicator means in continuity and voltage testing in said continuity and voltage test modes respectively, said indicator means being protected from externally initiated current flow in response to connection of the test probes to a voltage source while the instrument is in continuity mode at least by said current limiting means of said series loop and said first impedance.

2. The apparatus of claim 1, in which said indicating means is an LED, said electrical supply is a battery and said current limiting means is a resistor, said first, second, third and fourth impedances being resistors.

3. The apparatus of claim 2, in which said first and third impedances are resistors of similar resistance approximately in the range of 1 M ohm and said current limiting means and second and fourth impedances are resistors of resistance value approximately one-half that of said first and third resistors.

4. The apparatus of claim 3, in which said electronic switch means comprises a Darlington transistor, said switch means comprising a double-pole, double-throw switch having movable contacts, one of which connects through said first resistance to said one test probe and is shiftable to selectively connect said first resistance in the voltage test mode to the common point of said second and third resistances and in said continuity test mode to said control electrode, said switch having a further movable contact connected to said other test probe and in said voltage test mode connectible through said fourth resistance to said control electrode and in said continuity test mode conductively to said series loop between said electrical supply and protective resistance.

5. A portable instrument for checking electrical continuity, voltage and polarity, comprising in combination:

electronic switch means having a control electrode and main current electrodes controlled thereby;

current limiting means in series with said main electrodes and an LED serially interposed between said current limiting means and said electronic switch means and poled for conduction in series with the latter to provide a visible test indication;

portable electrical supply means connected across the series current limiting means, LED and main electrodes so as to provide operating current for said LED in both voltage and continuity test modes of the instrument upon conduction of said electronic switch means;

first and second test probes and a first resistance in series with said second test probe;

switch means actuable to a voltage test position in which said second test probe connects through said first resistance to a point between said electrical supply and the adjacent one of said main electrodes and including means connecting said first test probe to said control electrode, said switch means being actuable to a continuity test position and including means in such continuity test position connecting said second test probe through said first resistance to said control electrode and connecting said first test probe conductively to the junction point of said electrical supply and current limiting means;

whereby said electrical supply can actuate said control electrode by conduction through a conductive test member contacted by said probes and said first resistance so as to cause indicating current flow through said main electrodes and indicating means, but wherein a voltage source if erroneously connected across said test probes with said switch means in said continuity position can supply only a limited magnitude of current through said LED, to the extent permitted by said current limiting means and first resistance.

6. A portable instrument for testing electrical continuity, voltage and polarity, comprising in combination:

a substantially rectilinear casing having a forward extension for mounting a first conductive probe and a second conductive probe communicating with said casing through an elongate conductor, said casing comprising upper and lower substantially rectilinear, cup-shaped shells with opposed perimetral walls whose opposed edges are provided with complementary relief and lip portions extending through the rectilinear and extension portions of the casing shells to positively register the shells with respect to each other when brought together to form said casing, said casing further including dam means along lengths of said relief portions to facilitate adhesive joining of said casing shells to each other, said casing further including means dividing same into a forward compartment communicating with said forward extension and a rearward compartment;

a printed circuit board configured for a snug lateral fit within said forward compartment just inboard of said lip and relief portions, said shells having opposed upstanding ribs extending laterally into said forward compartment and of length to snugly grip the perimetral portion of the printed circuit board therebetween with said shells assembled, so as to positively locate said printed circuit board within said forward compartment, and conductive means extending from said board into said forward extension and electrically connected to said first probe supported in and extending forward from said extension;

battery leads extending from said circuit board into said rear compartment, said rear compartment housing fins extending laterally thereinto from the side walls of said shells for snugly locating a battery in said rearward compartment, the fins of one said shell being notched for guiding said elongate conductor from said circuit board out of the casing to the second probe, said casing further including means for opening said rearward compartment to permit insertion or removal of a battery;

said circuit board supporting electronic switch means and a visible indicator and current limiting means all connected in series with said battery leads for flowing indicator energizing current through said indicator upon actuation of said electronic switch means and means in one said casing shell rendering said indicating means visible from outside said casing, a manually actuable switch on said circuit board and means in one said casing shell rendering said switch actuable from outside said casing, and a four element resistance network and means interconnecting same with a control electrode of said electronic switch means, said manual switch, and the conductors leading to said probes for arranging a combination of three said resistors in the control electode circuit of said electronic switch means in one position of said manually actuable switch means but arranging a different combination of three of said resistors in the control electrode circuit of said electronic switch means in a second position of actuation of said manual switch means, said manual switch means being shiftable between a continuity test position and a voltage test position and in said continuity test position providing for series connection with said probes and indicator of a high resistance including said current limiting means and at least one of said four resistors.