METHOD AND APPARATUS FOR MEASURING THE AVERAGE LIQUID FLOW OF A RECIPROCATORY PUMP

• US 3,872,723 A
• Filed: 12/19/1973
• Issued: 03/25/1975
• Est. Priority Date: 12/28/1972
• Status: Expired due to Term

• Current Assignee: Ulrich Busch
• Original Assignee: Ulrich Busch
• Inventors: Busch, Ulrich
• Primary Examiner(s): Gill, James J.
• Assistant Examiner(s): Ciarlante, Anthony V.
• Application Number:
  US05/426,416
• Time in Patent Office: 461 Days
• Field of Search: 73/194R,199,198,223,206
• US Class Current: 73/168
• CPC Class Codes: G01F 1/00 Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow measuring a proportion of the volume flow G01F5/00
• CPC Class Codes: G01F 1/72 Devices for measuring pulsing fluid flows
• CPC Class Codes: G01F 15/024 involving digital counting
• CPC Class Codes: G01F 15/063 using electrical means

Abstract

A liquid storage means and a flow passage resistant means are connected between a reciprocatory pump and the input to a liquid chromatography system. The pressure variations caused by the pumping action induce proportional variations of the storage volume of the liquid storage means. These pressure variations are sensed and supplied to a signal processing means which includes a differentiating circuit. The movement of the plunger of the pump is scanned in order to derive timing signals related to a certain portion of the pump cycle. These timing signals control the signal processing means such that output signals are obtained which are related to the pressure drop of the liquid storage means during said portion of the pump cycle. The output signals are indicative of the average liquid flow being pumped.

Claims

1. Apparatus for measuring the liquid flow rate pumped by a cyclically operable, reciprocating pump having feed and return strokes, especially for use with gradient elution by a liquid chromatographic device, said apparatus comprising:

liquid storage means and liquid flow resistant means connected to the output of said pump, said liquid storage means having a volume substantially proportional to the pressure applied thereto by the liquid being pumped; and

a capacitance C defined by the change in volume with said applied pressure;

said liquid flow resistant means having a resistance R to the flow of liquid;

wherein the RC time constant resulting from the product of said resistance and capacitance is greater than the cycle time of said reciprocating pump;

means for sensing the variations in pressure exerted on said liquid storage means by the liquid being pumped;

timing means for producing timing signals related to the return stroke of said reciprocating pump; and

signal processing means responsive to the outputs of said sensing means and said timing means for producing a signal representative of said variations in pressure during at least a portion of the return stroke of said pump, said last named signal being indicative of the flow rate of the pumped liquid.

2. Apparatus as in claim 1, wherein the capacitance C of the liquid storage means as defined by the change in volume related to applied pressure is substantially constant over the range of the sensed pressure variations.

3. Apparatus as in claim 2, wherein the signal processing means includes a differentiating circuit coupled to the outputs of said pressure sensing means and said timing means, said differentiating circuit providing an output signal representative of the pressure variations related and synchronized to the return strokes of the pump.

4. Apparatus as in claim 1, wherein said liquid flow resistant means is connected to receive the liquid flow from the output of said liquid storage means.

5. Apparatus as in claim 1, wherein the liquid storage means, the liquid flow resistant means and the signal processing means are coupled between the pump and a liquid chromatographic device.

6. Apparatus as in claim 1, wherein the timing signals supplied by the timing means define a part of the time interval of the return stroke of the pump.

7. Apparatus as in claim 1, wherein the signal processing means includes sample-and-hold means for storing the values of several sequential pressure drops at the liquid storage means during sequential return strokes of the pump.

8. Apparatus as in claim 1, wherein the signal processing means includes means for rectifying the signals which correspond to the pressure variations at the liquid storage means, thereby to provide an output signal which is indicative of the average liquid flow rate.

9. Apparatus as in claim 1, wherein the liquid storage means comprises a device having a measuring chamber and a counter pressure chamber separated from the measuring chamber by a diaphragm, said measuring chamber having input and output channels for passing the liquid for which the flow rate is to be measured, the total volume of the measuring chamber and the input and output channels being substantially zero, except during application of pressure to the measuring chamber.

10. Apparatus as in claim 9, wherein the volume of the measuring chamber and the input and output channels in the non-pressured condition is substantially smaller than the quotient of the capacitance C of the liquid storage means and the compressibility factor of the liquid.

11. Apparatus as in claim 9, wherein the pressure sensing means is coupled to the counter pressure chamber.

12. Apparatus as in claim 9, wherein the measuring chamber contains a flat annular groove which extends circumferentially and in proximity to the edge of the diaphragm and which is connected to the input and output channels for the liquid being pumped.