Electromagnetic flowmeters

Claim 1

An electromagnetic flowmeter comprising: a detector head for sensing, and for producing signals representative of, flow rate of a medium; an amplifier supplied with said flow rate representative signals for amplifying them; and an indicator supplied with said amplified signals from said amplifier for producing indications of said flow rate; said indicator being calibrated to provide indications of flow rate as a function of the magnitude of a calibrating input signal thereto; said amplifier being calibrated to produce a predetermined output signal for a given input signal thereto; and a gain-modifying element operatively connected in said amplifier and removable from and insertable into said amplifier as a unit, said gain-modifying element being settable to different conditions as to produce corresponding different values of amplification by said amplifier; said gain-modifying element being identified as associated with said head and preset in accordance with the electrical characteristics of said head, prior to insertion into said amplifier, to modify the amplification of said amplifier so that the output signal from said amplifier applied to said indicator is of the magnitude to produce indications properly indicative of said rate of flow, whereby said amplifier, said indicator, or the combination of said head and said gainmodifying element may be replaced without requiring recalibrating of the flow meter; said head including a circuit for providing supply current to operate said head, and transformer means having a primary connected to sense the magnitude of said supply current, whereby a voltage having a magnitude representative of said current magnitude is produced across the secondary of said transformer; in which said voltage is applied to said amplifier to control its amplification as a function of the magnitude of said supply current; and wherein said gain-modifying element comprises resistive means connected in parallel with said transformer secondary when said element is inserted into said amplifier. p

Claim 3

The method of providing calibrated flowmeters and of replacing parts thereof without requiring recalibration of the flowmeter, wherein said flowmeter is of the type comprising a detector head for sensing, and for producing signals representative of, the rate of flow of a medium past said head, an amplifier supplied with said signals for producing an amplified output signal in response thereto, and an indicator supplied with said output signals to produce indications of said rate of flow, said method comprising the steps of: fabricating a plurality of standard amplifiers all having substantially the same nominal amplification characteristics, and each adapted to have connected therein a gain-modifying element which, when so connected, modifies the gain of the amplifier in a manner determined by the characteristics of said element so as to produce an output signal of predetermined value in response to an input signal of predetermined value applied to said amplifier; calibrating a plurality of indicators similarly, in response to the same test input signal, to provide rate-of-flow indications thereon as a function of said test input signal; fabricating a plurality of detector heads having similar but differing characteristics; fabricating a plurality of separately settable gain-modifying elements each adapted to be removably connected to any of said plurality of amplifiers to modify the amplification thereof according to the setting of the particular gain-modifying element so connected; setting each one of said gain-modifying elements so that, when a particular corresponding one of said detector heads is connected through one of said standard amplifiers to one of said calibrated indicators, and when said one gain-producing element is operatively connected to said one amplifier, said one indicator indicates properly the rate of flow of a medium past said detector head; providing identification associating each of said gain-modifying elements with the corresponding detector head with reference to which it was set; assembling one of said amplifiers, one of said indicators, and one of said gain-modifying elements with the corresponding one of said detector heads, into an operative flowmeter; and replacing the gain-modifying element and detector head in said assembled flowmeter with another of said plurality of gain-modifying elements and with the corresponding associated head.

Claim 4

The method of providing calibrated flowmeters and of replacing parts thereof without requiring recalibration of the flowmeter, wherein said flowmeter is of the type comprising a detector head for sensing, and for producing signals representative of, the rate of flow of a medium past said head, an amplifier supplied with said signals for producing an amplified output signal in response thereto, and an indicator supplied with said output signals to produce indications of said rate of flow, said method comprising the steps of: fabricating a plurality of standard amplifiers all having substantially the same nominal amplification characteristics, and each adapted to have connected therein a gain-modifying element which, when so connected, modifies the gain of the amplifier in a manner determined by the characteristics of said element so as to produce an output signal of predetermined value in response to an input signal of predetermined value applied to said amplifier; calibrating a plurality of indicators similarly, in response to the same test input signal, to provide rate-of-flow indications thereon as a function of said test input signal; fabricating a plurality of detector heads having similar but differing characteristics; fabricating a plurality of separately settable gain-modifying elements each adapted to be removably connected to any of said plurality of amplifiers to modify the amplification thereof according to the setting of the particular gain-modifying element so connected; setting each one of said gain-modifying elements so that, when a particular corresponding one of said detector heads is connected through one of said standard amplifiers to one of said calibrated indicators, and when said one gain-producing element is operatively connected to said one amplifier, said one indicator indicates properly the rate of flow of a medium past said detector head; providing identification associating each of said gain-modifying elements with the corresponding detector head with reference to which it was set; assembling one of said amplifiers, one of said indicators, and one of said gain-modifying elements with the corresponding one of said detector heads, into an operative flowmeter; and replacing the gain-modifying element and detector head in said assembled flowmeter with another of said plurality of gain-modifying elements and with the corresponding associated head.