Electronically controlled direct injection foam delivery system with temperature compensation

1. A unit of fire fighting equipment having a direct injection foam delivery system, comprising:

a water pump for pumping water through a first pipe;

a foam pump for pumping foam through a second pipe;

a mixing chamber having a first input coupled for receiving the water and a second input coupled for receiving the foam and an output for producing a water and foam mixture;

a control unit;

a first conductivity sensor for monitoring conductivity of the water and foam mixture and providing a first electrical signal to the control unit;

a second conductivity sensor for monitoring conductivity of the water and providing a second electrical signal to the control unit, wherein the control unit controls the foam pump in response to a difference between the first electrical signal and second electrical signal;

a flow meter monitors flow rate of the water and provides a third electrical signal to the control unit which in turn controls the foam pump in response to the third electrical signal; and

a temperature sensor monitors the water and provides a fourth electrical signal to the control unit wherein:

the control unit controls the foam pump flow for changes in water conductivity resulting from changes in water temperature, and

the control unit applies a correction factor to the flow meter to account for changes in water viscosity resulting from changes in water temperature.

2. The unit of fire fighting equipment of claim 1 , wherein the flow meter includes a paddle wheel sensor having a plurality of paddles which rotate to sense water flow.

3. The unit of fire fighting equipment of claim 1 , wherein the control unit includes a microprocessor coupled for receiving the first, second, third, and fourth electrical signals and generating a control signal to regulate the foam pump and the flow meter.

4. The unit of fire fighting equipment of claim 1 , further including an operator control panel coupled to the control unit for inputting a water and foam mixing ratio.

5. The unit of fire fighting equipment of claim 1 , wherein the foam pump includes:

a first foam pump providing a first range of flow rates in response to the control unit and having an output coupled to the second pipe; and

a second foam pump providing a second range of flow rates in response to the control unit and having an output coupled to the second pipe, the second range of flow rates being greater than the first range of flow rates.

6. The unit of fire fighting equipment of claim 1 , further including:

a first foam tank for providing a first foam to the second pipe to mix with the water; and

a second foam tank for providing a second foam to the second pipe to mix with the water.

7. The unit of fire fighting equipment of claim 6 , wherein the control unit enables the first foam pump or the second foam pump to provide the foam to the second pipe.

8. A direct injection foam delivery system, comprising:

a water pump for pumping water through a first pipe;

a foam pump for pumping foam through a second pipe;

a mixing chamber having a first input coupled for receiving the water and a second input coupled for receiving the foam and an output for producing a water and foam mixture;

a control unit;

a first conductivity sensor for monitoring conductivity of the water and foam mixture and providing a mixture conductivity signal to the control unit;

a second conductivity sensor for monitoring conductivity of the water and providing a water conductivity signal to the control unit, wherein the control unit controls the foam pump in response to a difference between the mixture conductivity signal and water conductivity signal; and

a temperature sensor monitors the water and provides a temperature signal to the control unit wherein the control unit controls the foam pump flow to compensate for changes in water conductivity resulting from changes in water temperature.

9. The direct injection foam delivery system of claim 8 ,

comprising a flow meter coupled in-line with the water pump and having an output coupled to the control unit.

10. The direct injection foam delivery system of claim 9 , wherein the flow meter including a paddle wheel sensor having a plurality of paddles which rotate to sense water flow.

11. The direct injection foam delivery system of claim 9 , wherein the control unit includes a microprocessor coupled for receiving electrical signals and generating a control signal to regulate the foam pump.

12. The direct injection foam delivery system of claim 9 , further including an operator control panel coupled to the control unit for inputting a water and foam mixing ratio.

13. The direct injection foam delivery system of claim 8 , wherein the first conductivity sensor includes first and second plates positioned in the flow stream of the conduit for measuring conductivity of the water and foam mixture.

14. The direct injection foam delivery system of claim 8 , wherein the control unit further includes:

a first interface circuit coupled between the first conductivity sensor and the control unit for generating a voltage having dual polarity and a fifty percent duty cycle; and

a second interface circuit coupled between the second conductivity sensor and the control unit for generating a voltage having dual polarity and a fifty percent duty cycle.

15. A system for mixing first and second fluids, comprising:

a conduit including a mixing chamber for transporting the first fluid under pressure, wherein the second fluid is injected into the conduit at the mixing chamber for producing a mixture of first and second fluids;

a regulator for controlling a flow rate of the second fluid;

a first conductivity sensor coupled to the conduit for monitoring conductivity of the first and second fluid and providing a mixture conductivity signal to the regulator;

a second conductivity sensor coupled to the conduit for monitoring conductivity of the first fluid and providing a first fluid conductivity signal to the regulator, wherein the regulator controls the injection of the second fluid in response to a difference between the mixture conductivity signal and first fluid conductivity signal; and

a flow meter coupled to the conduit for monitoring a flow rate of the first fluid and providing a flow signal to the regulator which controls the injection of the second fluid at the mixing chamber in response to the flow signal.

16. The system of claim 15 , further including:

a first pump for pumping the first fluid through a first pipe;

a second pump for pumping the second fluid through a second pipe; and

a mixing chamber having a first input coupled for receiving the first fluid and a second input coupled for receiving the second fluid and an output for producing the mixture of first and second fluids.

17. The system of claim 16 , wherein the regulator includes:

a control unit coupled with the flow meter;

the flow meter coupled in-line with the first pump.

18. The system of claim 17 , wherein the flow meter including a paddle wheel sensor having a plurality of paddles which rotate to sense first fluid flow.

19. The system of claim 17 , wherein the control unit includes a microprocessor coupled for receiving electrical signals and generating a control signal to regulate the second pump.

20. The system of claim 17 , further including an operator control panel coupled to the control unit for inputting a first and second fluid mixing ratio.

21. The system of claim 16 , further including:

a temperature sensor that monitors the first fluid and provides a temperature signal to the regulator wherein:

the regulator controls the second pump for changes in conductivity of the first fluid resulting from changes in the temperature of the first fluid, and

the control unit applies a correction factor to the flow meter to account for changes in viscosity of the first fluid resulting from changes in temperature of the first fluid.

22. The system of claim 15 , wherein the first conductivity sensor includes first and second plates positioned in the flow stream of the conduit for measuring conductivity of the mixture of first and second fluids.

23. The system of claim 22 , wherein the regulator further includes:

a first interface circuit coupled between the first conductivity sensor and the control unit for generating a voltage having dual polarity and a fifty percent duty cycle; and

a second interface circuit coupled between the second conductivity sensor and the control unit for generating a voltage having dual polarity and a fifty percent duty cycle.

24. A method of injecting foam into water flow, comprising:

pumping water through a first pipe;

pumping foam through a second pipe;

mixing the water and foam to produce a water and foam mixture;

monitoring flow rate of the water;

sensing temperature of the water; and

regulating the water and foam mixture, wherein the regulation includes:

adjusting foam pumping flow to compensate for changes in water conductivity resulting from changes in water temperature, and

adjusting the flow meter to account for changes in water viscosity resulting from changes in water temperature.

25. The method of claim 24 , wherein the regulation includes:

monitoring conductivity of the water and foam mixture; and

monitoring conductivity of the water; and

adjusting a flow rate of the foam pump in response to a difference between the conductivity of the water and conductivity of the water and foam mixture.