Exposure meter for thermal imaging devices

Claim 2

A process for determining appropriate exposure for thermographic reproduction from a document contain-ing information to be reproduced, said information being in the form of infrared-absorptive indicia which, upon exposure to infrared radiation, converts absorbed energy to a thermal pattern corresponding to said information, comprising: providing a sheet of thermotropic material sensitive to a predetermined temperature to undergo a discernible and reversible modification of form; positioning said sheet of thermotropic material adjacent said document in sufficient proximity thereto to absorb heat from said thermal pattern; exposing said document to infrared radiation sufficient to generate said thermal pattern and effect discernible modification of said thermotropic material in correspondence to said generated thermal pattern; determining the level of exposure causing said modification; determining the appropriate level of a second infrared radiation exposure, for said thermographic reproduction, in view of said first mentioned level of exposure; and thermographically reproducing said information at said second level of said heat exposure.

Claim 3

The invention according to claim 1 in which said thermotropic material has electrical resistance which is sharply temperature dependent, exhibiting a marked decrease in electrical resistance at a predetermined temperature, and said first level of exposure is determined by monitoring the electrical resistance of said thermotropic material during said exposure.

Claim 4

The invention according to claim 1 in which said thermotropic material is cholesteric liquid crystalline material reflecting different wavelengths of light with change in temperature.

Claim 5

The invention according to claim 3 in which said first mentioned level of exposure is determined by exposing said cholesteric material to light and determining a change in the wavelengths of reflected portions thereof.

Claim 6

The inventIon according to claim 3 including the steps of predetermining said level of second infrared radiation exposure and determining a wavelength band of said reflected light corresponding to said predetermined level of second infrared radiation exposure, said first mentioned level of exposure being determined by exposing said cholesteric material to light of said wavelength band during said first mentioned exposure and determining the level of said exposure required for reflection of said wavelength band.

Claim 7

The invention according to claim 1 in which said thermotropic material comprises a thermochromic compound changing color at a predetermined temperature, and said first level of exposure is determined by measuring the time required for said color change.

Claim 8

The invention according to claim 1 in which said thermotropic material comprises opaque solid material which fuses at a predetermined temperature to a translucent form, and said first level of exposure is determined by measuring the time required for said fusion.

Claim 9

A thermal exposure meter for determining appropriate exposure for thermographic reproduction from a document containing information to be reproduced, said information being in the form of infrared-absorptive indicia which, upon exposure to infrared radiation, converts absorbed energy to a thermal pattern corresponding to said information, comprising: a sheet of thermotropic material sensitive to a predetermined temperature to undergo a discernible and reversible modification of form; means for supporting said document containing information to be reproduced; means for positioning said sheet of thermotropic material adjacent said document in sufficient proximity thereto to absorb heat from said thermal pattern; means for applying infrared radiation to said document sufficient to generate discernible modification of said thermotropic material in correspondence to said information; means for determining the level of exposure causing said modification; means for determining the appropriate level of a second infrared radiation exposure for said thermographic reproduction in view of said first mentioned level of exposure; and means for thermographically reproducing said information at said second level of said heat exposure.

Claim 10

A thermal exposure meter for determining appropriate exposure for thermographic reproduction from a document containing information to be reproduced, said information being in the form of infrared-absorptive indicia which, upon exposure to infrared radiation, converts absorbed energy to a thermal pattern corresponding to said information, comprising: a sheet of thermotropic material sensitive to a predetermined temperature to undergo a discernible and reversible modification of form; means for supporting said document containing information to be reproduced; means for positioning said sheet of thermotropic material adjacent said document in sufficient proximity thereto to absorb heat from said thermal pattern; means for applying infrared radiation to said document sufficient to generate discernible modification of said thermotropic material in correspondence to said information; means for determining the level of exposure causing said modification; means for determining the appropriate level of a second infrared radiation exposure for said thermographic reproduction in view of said first mentioned level of exposure; and means for thermographically reproducing said information at said second level of said heat exposure.

Claim 11

The invention according to claim 8 in which said thermotropic material comprises cholesteric liquid crystalline material reflecting different wavelengths of light with change in temperature, and said radiation applying means comprises means for applying a mixture of wavelengths in the infrared and visible spectral regions.

Claim 12

The invention according to claim 8 in which said thermotropic material comprises thermochromic material changing color at a predetermined temperature, and said radiation applying means comprises means for applying a mixture of wavelengths in the infrared and visible spectral regions.

Claim 13

The invention according to claim 8 in which said thermotropic material comprises opaque solid material which fuses at a predetermined temperature to a translucent form, and said radiation applying means comprises means for applying a mixture of wavelengths in the infrared and visible spectral regions.

Claim 14

The invention according to claim 8 in which said thermotropic material comprises material having electrical resistance which is sharply temperature dependent for exhibiting a marked decrease in electrical resistance at a predetermined temperature, and said discerning means comprises means for monitoring the electrical resistance of said thermotropic material.