Strain-gage transducer bridge gages with integral calibration resistors
First Claim
1. A strain-gage transducer bridge gage unit for a transducer having a sensing portion exhibiting surface strains in response to loading thereof, comprising a relatively thin broad-area insulating carrier having a thin metal layer thereon shaped to form both at least a pair of strain gages and a calibration resistor thereon which are integral with one another and with relatively large-area wiring tabs, active portions of said strain gages and said calibration resistor being spaced apart laterally along said carrier to occupy separate positions and to have predetermined orientations promoting response to surface strains and immunity from effects of surface strains, respectively, when said carrier is bonded with predetermined surfaces of a sensing portion of a transducer, said calibration resistor being directly connected integrally at one end with one of said tabs and at its other end with a junction of each of two of said strain gages, whereby said calibration resistor is disposed for electrical wiring externally of a strain gage bridge including said strain gages and calibrates external impedance characteristics of a bridge, said calibration resistor exhibiting resistance which does not vary significantly with temperature over an intended range of use.
2 Assignments
0 Petitions
Accused Products
Abstract
Each of two pairs of electrical-resistance strain gages which are to make up a measurement bridge for a beam-type load cell is fashioned as a composite wherein two spaced-apart grids of foil-type parallel elongated filaments oriented and functioning as strain gages are made of material promoting a strain gage factor effective to compensate for elastic modulus change of the beam material as temperature varies over an expected range. Intermediate the two grids of strain-gage filaments, where a neutral position between tension and compression surface strains of the sensing element of a gaged beam may be expected to appear, the common insulating backing for the two grids carries a set of narrow strands which produce a dummy foil resistance of predetermined value needed for a calibration wherein it simulates the influence upon bridge input impedance of a temperature-compensation resistance such as would otherwise be used without the inherent compensation for elastic modulus changes by way of offsetting effects of strain gage factor of the gages. The same material which forms the foil or printed-circuit type gage grids also forms the dummy or calibration resistor upon the same underlying backing, and, in addition creates relatively large-area and low-resistance integral interconnections between the gages and resistance and tabs for needed external-wiring connections.
14 Citations
8 Claims
- 1. A strain-gage transducer bridge gage unit for a transducer having a sensing portion exhibiting surface strains in response to loading thereof, comprising a relatively thin broad-area insulating carrier having a thin metal layer thereon shaped to form both at least a pair of strain gages and a calibration resistor thereon which are integral with one another and with relatively large-area wiring tabs, active portions of said strain gages and said calibration resistor being spaced apart laterally along said carrier to occupy separate positions and to have predetermined orientations promoting response to surface strains and immunity from effects of surface strains, respectively, when said carrier is bonded with predetermined surfaces of a sensing portion of a transducer, said calibration resistor being directly connected integrally at one end with one of said tabs and at its other end with a junction of each of two of said strain gages, whereby said calibration resistor is disposed for electrical wiring externally of a strain gage bridge including said strain gages and calibrates external impedance characteristics of a bridge, said calibration resistor exhibiting resistance which does not vary significantly with temperature over an intended range of use.
- 4. A strain-gage transducer bridge gage unit for a transducer having a sensing portion exhibiting surface strains in response to loading thereof, comprising a relatively thin broad-area insulating carrier having a thin metal layer thereon shaped to form both strain gage means and calibration resistor means thereon which are integral with one another and with relatively large-area wiring tabs, active portions of said strain gage means and said calibration resistor means being spaced apart laterally along said carrier to occupy separate positions and to have predetermined orientations promoting response to surface strains and immunity from effects of surface strains, respectively, when said carrier is bonded with predetermined surfaces of a sensing portion of a transducer, said material of said layer imparting to said strain gage means a gage factor changeable with temperature and thereby causes the transducer bridge including the unit with said strain gage means to develop outputs in which tendencies toward changes with temperature due to modulus-of- elasticity variations of the sensing portion of the transducer are substantially offset by tendencies toward changes with temperature due to gage-factor variations of said strain gage means, said calibration resistor means exhibiting resistance which does not vary significantly with temperature over an intended range of use.
-
8. A strain-gage transducer having rigid portions in load-transmitting relationship with an elastically-deformable sensing portion which exhibits surface strains in response to loading thereof, at least one composite gage unit for sensing said surface strains and for introducing calibration resistance into circuit relationship with a strain-gage bridge network, said gage unit including an insulating carrier having a metallic foil layer thereon shaped to form at least one strain-gage grid and at least one calibration resistor thereon which are integral with one another and with relatively large-area wiring tabs, active portions of said grid and resistor being spaced apart laterally along said carrier to occupy separate positions and to have predetermined orientations in relation to said sensing portion which promote response to surface strains and immunity from effects of surface strains, respectively, means connecting said strain-gage grid into a strain-gage bridge network with said calibration resistor in series with the input thereto, said metallic layer being of an alloy essentially of nickel, chromium and aluminum which causes said strain-gage grid to promote changes in outputs from said bridge network which tend to offset changes in outputs due to changes with temperature of the modulus of elasticity of the material of the sensing portion of the transducer, and said resistor exhibiting resistance which augments input impedance of said bridge network and raises it toward a predetermined value.
Specification