Pump operating state without the use of traditional measurement sensors

• US 20030129062A1
• Filed: 01/09/2002
• Published: 07/10/2003
• Est. Priority Date: 01/09/2002
• Status: Active Grant

• Current Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Original Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Inventors: Erickson, Barry, Sabini, Eugene P., Lorenc, Jerome A.
• Granted Patent: US 6,776,584 B2
• Time in Patent Office: Days
• US Class Current: 417/22
• CPC Class Codes: F04D 15/0088 Testing machines

Abstract

A method for determining whether a centrifugal pump is operating within its normal flow operating range includes the steps: of determining a motor torque/TDH relationship over a range of speeds for a minimum flow rate in order to obtain a minimum flow operating range for the centrifugal pump; determining a motor torque/TDH relationship over a range of speeds for a maximum flow rate in order to obtain a maximum flow operating range for the centrifugal pump; determining the actual operating motor torque and TDH of the centrifugal pump at a given operating point; and determining whether the actual operating motor torque and TDH of the centrifugal pump fall within the minimum flow and maximum flow operating ranges of the centrifugal pump.

Claims

1. A method of determining the operating point of a centrifugal pump having a given hydraulic performance characteristic comprising the steps of:

measuring at least two independent pump variables capable of determining the operating point of said pump by,

first measuring said two independent variables at least a first pump rotational speed, and

second measuring said two independent variables at at least a second different pump rotational speed,

processing said measured variables as measured at each speed to provide two sets of data indicative of the operating point of said pump.

2. The method according to claim 1 wherein said given hydraulic characteristic is obtained at both the minimum and maximum continuous flow for the impeller diameter of the centrifugal pumps, the speed (N) total dynamic head (TDH) and pump efficiency to compute the Brake Horsepower (BHP) by computing:

3. The method according to claim 2 wherein said two variables are pump motor torque (T) and pump motor speed (N).

4. The method according to claim 3 wherein the pump motor torque is computed at a first speed N₁ and a second speed N₂ by computing:

5. The method according to claim 4 wherein said step of processing includes computing:

6. The method according to claim 1 wherein said operating point is determined according to maximum and minimum flow at any pump speed.

7. Apparatus for determining the operating point of a centrifugal pump, comprising:

a centrifugal pump having a rotating impeller coupled to a drive shaft for pumping fluid by centrifugal force,

a motor coupled to said drive shaft operative to rotate said drive shaft and therefore said impeller at a selected rotational speed,

a variable speed drive circuit coupled to said motor and operative to vary said selected speed to operate said motor at any one of a plurality of selected speeds,

said motor producing different values for motor variables at each selected speed,

a processor responsive to each speed to process said selected motor values provided at each speed to provide an output indicative of the operational point of said motor by computing at least two variables at said different speeds using the pump Affinity Laws.

8. The apparatus according to claim 7 wherein said at least two variables are Motor Torque (T) and total dynamic head (TDF).

9. The apparatus according to claim 8 wherein said processor has stored therein the Brake Horsepower (BHP) of said centrifugal pump.

10. The apparatus according to claim 9 wherein said processor operates to compute said Torque (T) and total dynamic head (TDH) by solving the following equation:

11. The apparatus according to claim 7 wherein said speed measurements are made at the minimum and maximum flow points.

12. The apparatus according to claim 7 wherein said pump further includes a flow sensor and a pump differential transducer.

13. A method for determining whether a centrifugal pump is operating within in a normal operating range comprising the steps of:

determining the actual operating point of the centrifugal pump based on motor torque and motor speed; and

comparing the actual operating point of the centrifugal pump to minimum and maximum flow operating ranges of the centrifugal pump to determine whether the centrifugal pump is operating within minimum flow and maximum flow operating ranges.

14. A method for determining whether a centrifugal pump is operating in a normal operating range comprising the steps of:

determining a hydraulic performance curve for a minimum continuous flow rate in order to obtain a minimum flow operating range for the centrifugal pump;

determining a hydraulic performance curve for a maximum flow rate in order to obtain a maximum flow operating range for the centrifugal pump;

computing a torque for said maximum operating range a torque for said minimum operating range;

computing the torque and TDH at different operating speeds;

determining the motor operating point by processing the computed values.