Electronic chemical trace detector

Abstract

A hotplate chemical trace detector comprising a heatable conducting plate with a heater element having a predetermined temperature-power characteristic. A balancing circuit comprises an adjustable resistor for tuning the heater element to a predefined resistor value. A processor is provided for adjusting the adjustable resistor so as to provide a stabilized temperature in said heatable conducting plate and a detection circuit is provided for detecting a change of resistance in the heatable conducting plate in accordance with the presence of a chemical trace reacting in the presence of the conducting plate. According to the invention a test circuit is provided for measuring a dissipated power in the heater element and for calculating a real temperature from the dissipated power in the heater element based on the predetermined temperature-power characteristic.

1 - 9 . (canceled) 
     
     
         10 . A method of calibrating a hotplate chemical trace detector comprising a heater plate tunable by an adjustable resistor, comprising:
 placing the sensor in a preconditioned neutral ambiance;   providing a predetermined power to the heater plate;   relating the predetermined power in the heater plate to a set temperature using a temperature-power characteristic of the heater plate; and   zeroing the adjustable resistor to a preset value relating to the set temperature.   
     
     
         11 . The method according to  claim 10 , wherein the method further comprises using an estimated resistance-temperature characteristic of the heater plate for presetting predetermined resistance values of the adjustable resistor. 
     
     
         12 . A method of identifying a chemical substance on a hotplate sensor comprising a adjustable resistance of a heater element heater element having predetermined temperature-power relationship comprising;
 presetting a predetermined temperature to a hotplate using an adjustable resistance of a heater element;   measuring a dissipated power in the heater element;   comparing a measured dissipated power to an estimated power using the predetermined temperature-power relationship and relating a measured power difference to a reaction energy of a combination of chemical substances reacting on the hotplate; and   identifying said chemical substance based on said measured power difference.   
     
     
         13 . A method of calibrating a hotplate chemical trace detector comprising:
 providing a heatable conducting plate comprising a heater element having a predetermined power-temperature characteristic;   providing a balancing circuit comprising an adjustable resistor for tuning the heater element to a predefined resistor value;   providing a processor for adjusting the adjustable resistor so as to provide a stabilized temperature in said heatable conducting plate;   providing a detection circuit for detecting a change of resistance in the heatable conducting plate in accordance with the presence of a chemical trace reacting in the presence of the conducting plate;   providing a test circuit for measuring a dissipated power in the heater element and for calculating a real temperature from the dissipated power in the heater element based on the predetermined power-temperature characteristic;   placing the trace detector in a preconditioned neutral ambiance;   providing power to the heatable conducting plate having the predetermined power-temperature characteristic;   measuring, via said test circuit, the power provided to the heatable conducting plate;   relating the measured power in the heatable conducting plate to a set temperature using the power-temperature characteristic of the heatable conducting plate; and   zeroing the adjustable resistor of the balancing circuit to a preset value relating to the set temperature.   
     
     
         14 . The method according to  claim 13 , wherein the method further comprises using an estimated resistance-temperature characteristic of the heatable conducting plate for presetting predetermined resistance values of the adjustable resistor.