Method and means for equalizing the measuring sensitivity of a plurality of strain gage transducers

• US 4,556,115 A
• Filed: 06/17/1983
• Issued: 12/03/1985
• Est. Priority Date: 06/17/1983
• Status: Expired due to Term

• Current Assignee: Hottinger Baldwin Measurements, Inc. (Spectris PLC)
• Original Assignee: Hottinger Baldwin Measurements, Inc. (Spectris PLC)
• Inventors: Lockery, Harry E., Freymiller, Edward
• Primary Examiner(s): MILLER JR, GEORGE
• Application Number:
  US06/505,395
• Time in Patent Office: 900 Days
• Field of Search: 177/50, 177/1, 177/211, 73/862.67, 73/1 B
• US Class Current: 177/211
• CPC Class Codes: G01G 3/142 Circuits specially adapted therefor

Abstract

The load measuring sensitivities of transducers, such as beam type transducers, or the like, are desensitized by connecting a desensitizing resistance in series with the strain gages attached to a transducer so that these desensitizing resistances become part of the respective bridge arm in which the corresponding strain gage is located. In a group of four transducers, each carrying, for example two strain gages, the transducer which has the lowest sensitivity is ascertained. Thereafter, the sensitivities of the other three transducers are reduced by the desensitizing resistors connected directly in series with the strain gages in the other three transducers so that all have substantially the same sensitivity as the mentioned lowest initial sensitivity in the group of transducers. Any influences of these desensitizing resistors from one bridge arm to another bridge arm are considered in the derivation of the correct desensitizing resistances. Thereafter, a further sensitivity equalization may be achieved by mechanically increasing the sensitivity of those transducers in the group still having a lower sensitivity than the lowest sensitivity transducer in the group. Such mechanical sensitivity increase involves removing material from the sensing portion of a transducer for example by filing or grinding until all transducers of a group have the same sensitivity within an acceptable tolerance range, for example, 0.02%.

Claims

1. A method for desensitizing the load measuring sensitivities of a plurality of strain gages forming at least two full bridge circuits relative to each other to provide uniform load measuring sensitivities with due regard to a shunting interacting effect resulting when said strain gages are electrically interconnected for forming at least two pairs of half bridges which in turn are electrically interconnected to form said at least two full bridges, said strain gages being secured in pairs to at least four load measuring beams forming a load measuring device, comprising the following steps:

(a) successively applying a standardized load to each of said load measuring beams for determining the strain gage pairs having the lowest sensitivity and the strain gage pairs having higher sensitivities relative to said lowest sensitivity;

(b) determining, by calculation, a sensitivity change value representing said shunting interacting effect resulting from connecting at least two pairs of half bridges in parallel to each other to form said at least two paralleled full bridges,

(c) calculating, by taking into account said higher sensitivities and said sensitivity change value, for each strain gage pair having a higher sensitivity than said lowest sensitivity, desensitizing resistances to be connected in series with the respective one of said strain gage pairs having a higher sensitivity for reducing the respective higher sensitivity and for neutralizing said shunting interacting effect, and

(d) electrically connecting said calculated desensitizing resistances in series with the respective strain gage pairs for achieving said desensitizing of said strain gages and said neutralizing of said shunting interacting effect, simultaneously.

2. In a bridge circuit arrangement for measuring loads with the aid of sensing beams having strain gages attached to said load sensing beams, comprising at least four sensing beams each carrying a pair of strain gages for a total of eight strain gages forming eight bridge arms electrically connected to form at least two pairs of half bridges which in turn are electrically connected in parallel to each other to form at least full bridges, each half bridge comprising a tension sensing strain gage and a compression sensing strain gage forming a pair, the improvement comprising desensitizing resistors electrically connected in series directly with said strain gages in said bridge arms, said desensitizing resistors being calculated for reducing the load sensitivity of at least certain strain gages down to the lowest load sensitivity of one strain gage in a group, said desensitizing resistors being further calculated for neutralizing a shunting interacting effect which results due to the parallel connection of two half bridges forming a pair.