Liquid level detection circuit for control of liquid level responsive device

A liquid presence detection circuit for detecting the presence or absence of a liquid and controlling a load response thereto, said circuit comprising:

• a selectively triggerable thyristor serially connected with a load, one side of said thyristor/load series circuit connected to one side of a source of alternating power and the other side thereof connected to the other side of the source of alternating power, said thyristor triggered into conduction in response to a trigger voltage applied to a trigger input thereof;
• a liquid presence probe including at least first and second spaced apart electrical contacts, said first contact connected to one side of said thyristor/load series circuit through a first voltage divider circuit and said second contact connected to the other side of said thyristor/load series circuit through a second voltage divider circuit;
• both said first and said second voltage divider circuits including at least first and second series connected resistance elements;
• and
• a trigger circuit for triggering said thyristor into conduction in response to the presence of a liquid between said first and said second contacts of said probe to thereby provide electrical energy to said load, said triggering circuit including a first SCR and a second SCR, said first and second SCR's connected anode-to-cathode with one of said anode-to-cathode connections connected to the trigger input of said thyristor and the other of said anode-to-cathode connections connected to the other side of said thyristor/load series circuit;
• a gate input of said first and said second SCR's connected, respectively, to intermediate points of said first and said second voltage divider circuits.

A liquid cooled, wet-niche lamp structure for providing underwater illumination in a liquid-containing pool or the like and protected against over-temperature operation incident to a low-liquid condition, said lamp structure comprising:

• a lamp housing adapted to receive an illuminatable lamp therein;
• said lamp adapted to be supported in heat exchange relationship with a surrounding liquid media to effect cooling thereof and having a power circuit for connection to an alternating source of electrical power;
• a liquid presence probe exposed to the liquid including first and second spaced apart contacts for detecting the presence or absence of a liquid,
• control circuit means connected to said liquid presence probe and the lamp for providing electrical power to the lamp in the presence of the liquid cooling media and interrupting the flow of electrical power to the lamp in the absence of the liquid cooling media, said control circuit including
• a triggerable thyristor in series circuit with the lamp, said thyristor/lamp series circuit connectible across the power circuit, said thyristor triggerable into conduction to cause a flow of power through the lamp in response to a trigger signal applied to a trigger input thereof;
• a trigger circuit for triggering said thyristor including first and second SCR's connected anode-to-cathode with the first of said anode-to-cathode connections connected to said trigger input and the other of said anode-to-cathode connections connected to said thyristor/lamp series circuit, each of said SCR's including a gate input, the gate input of said SCR's connected, respectively, to first and second spaced apart contacts;
• and
• resistance means connected to said thyristor/lamp circuit and said first and second contacts to provide a voltage potential across said first and second contacts;
• whereby the presence of a liquid bridging said contacts successfully gates the SCR's to thereby trigger the thyristor into conduction.

A liquid cooled, wet-niche lamp structure for providing underwater illumination in a liquid containing pool or the like and protected against over temperature operation incident to a low-liquid condition, said lamp structure comprising:

• a lamp housing adapted to receive an illuminatable lamp therein;
• said lamp adapted to be supported in heat exchange relationship with a surrounding liquid media to effect cooling thereof and having a power circuit for connection to an alternating source of electrical power;
• control circuit means for providing electrical power to the lamp in the presence of the liquid cooling media and interrupting the flow of electrical power to the lamp in the absence of the liquid cooling media, said control circuit including
• a selectively triggerable thyristor serially connected with said lamp, one side of said thyristor/lamp series circuit connected to one side of the source of power and the other side thereof connected to the other side of the source of power, said thyristor triggered into conduction in response to a trigger voltage applied to a trigger input thereof;
• a liquid presence probe including at least first and second spaced apart electrical contacts, said first contact connected to one side of said thyristor/lamp series circuit through a first voltage divider circuit and said second contact connected to the other side of said thyristor/lamp series circuit through a second voltage divider circuit;
• both said first and second voltage divider circuit including at least first and second series connected resistance elements;
• and
• a trigger circuit for triggering said thyristor into conduction in response to the presence of a liquid between said first and said second contacts of said probe to thereby provide electrical energy to said lamp, said triggering circuit including a first SCR and a second SCR, said first and said second SCR's connected anode-to-cathode with one of said anode-to-cathode connections connected to the trigger input of said thyristor and the other of said anode-to-cathode connections connected to the other side of said thyristor/lamp series circuit, a gate input of said first and said second SCR's connected, respectively, to intermediate points of said first and said second voltage divider circuits.