Thermal measuring and testing – Differential thermal analysis
Reexamination Certificate
1999-09-24
2001-11-20
Hirshfeld, Andrew H. (Department: 2859)
Thermal measuring and testing
Differential thermal analysis
C374S011000, C374S001000, C374S043000
Reexamination Certificate
active
06318890
ABSTRACT:
The present invention relates to a single cell calorimeter comprising a heat source, a sample holder having a sample position thermally coupled to said heat source to thereby establish a heat flow path for a flow of heat between said heat source and a sample in said sample position, and a controller for controlling the amount of heating by said heat source.
Calorimeters may be used for the thermal analysis of various kinds of materials. A sample of the material placed in the sample position is heated by the heat source and the flow of heat between the heat source and the sample is evaluated to thereby derive structural and compositional information about the material, in particular heat capacity, phase transitions, onset temperatures, etc. Conventionally, for the sake of accuracy and dynamic range differential methods, for instance differential scanning calorimetry (DSC), are being used. In these differential methods, a reference position is arranged in the heat flow calorimeter symmetrically with respect to the sample position and a temperature difference is measured between a sample at the sample position and a known reference material at the reference position. The need for the reference position in addition to the sample position undesirably increases the expenditure of construction. More-over, any symmetry deviation in heat conduction between the heat source on the one hand and the sample and reference positions, respectively, on the other hand is detrimental for the accuracy of measurement.
A calorimeter of the type having separate sample and reference positions to perform a differential measurement between a sample in the sample position and a reference material in the reference position is described in EP 0 559 362 A1. In this known calorimeter, the controller controls a temperature of the heat source in accordance with a predetermined temperature program so as to cause said heat source temperature to vary in correspondence with a linear rise of temperature superposed by a periodic temperature modulation. A deconvolution technique is used to evaluate the measured differential signal to thereby derive from said measured differential signal two separate signal components caused by the linearly changing component and the modulation component of the heat source temperature, respectively.
WO 95/33199 and WO 95/33200 similarly disclose calorimeters designed for differential measurement between a sample in a sample position and a reference material in a reference position. In both cases, a temperature of the heat source is driven through a predetermined temperature program, said temperature program comprising two linearly changing parts of the same time duration in the first case and a linearly changing part superposed by a periodically changing part in the second case. The measured differential signal and a phase difference between the measured differential signal and the programmed temperature of the heat source are evaluated to separately derive a real and an imaginary signal portion.
It is an object of the present invention to provide for a heat flow calorimeter of the single-cell type having a simplified construction with small response time, less power requirement, smaller temperature grading, and smaller dimension. It is a further object to remove difficulties caused by symmetry deviations in heat flow to the sample position and a reference position.
In order to attain these objects, the single cell calorimeter according to the present invention is characterized by means for measuring a temperature difference between at least two locations spaced at a distance along said heat flow path to thereby provide a signal representative of said temperature difference, signal source means for providing a compensation signal representative of a flow of heat along said heat flow path when a sample is not located at said sample position, and means for evaluating said flow of heat between said sample in said sample position and said heat source on the basis of said measured temperature difference signal and said compensation signal.
According to the present invention, by measuring the temperature difference along the heat flow path to the sample position, there is no need for a reference position in the heat flow calorimeter with a resultant remarkable simplification and size reduction of the overall construction. The compensation signal from the signal source means takes account for any portion of the heat flow along the heat flow path which is not caused by the presence of the sample in the sample position. This enables the evaluating means to obtain the net amount of heat flow into or out of the sample.
The terms “heating”, “heat flow”, “heat source” and related terms are to be understood in the context of the present specification to mean either heating or cooling. In the latter case, the “heat source” will for instance be a source of cooling agent thermally coupled to the sample position.
The compensation signal may be predetermined for each individual setting and construction of the heat flow calorimeter, in particular the type of a crucible used to accommodate the sample and/or the type of atmosphere used in the calorimeter. With these experimental settings being fixed, the compensation signal will still depend on temperature conditions in the calorimeter. For this purpose, in a preferred embodiment of the heat flow calorimeter, means for measuring a heating temperature of said heat source to thereby provide a signal representative of said measured heating temperature is provided, said signal source means being operative to generate said compensation signal in accordance with a function of said measured heating temperature signal. This function may for instance be predetermined on the basis of a mathematical model using the laws of thermodynamics and/or empirical data, in particular polynomial functions fitting such empirical data to a desired degree of accuracy.
Preferably, the invention may be realized in that said compensation signal provided by said signal source means is representative of a temperature difference between said at least two mutually spaced locations along said heat flow path when a sample is not located in said sample position. When embodying the signal source means in this manner, the net heat flow to the sample is proportional to the difference between the measured temperature difference signal and the compensation signal with the proportionality factor being the heat resistance along the heat flow path which may be determined by conventional calibration methods. In such an embodiment, the evaluating means therefore comprises means for deriving a difference between said measured temperature difference signal and said temperature difference signal from said signal source means.
Like in conventional calorimetry, it is desirable to drive the sample through heating programs varying temperature as a function of time. These temperature variations may be linear heating or cooling scans as is the case in conventional DSC. Further, such linear scans may have superimposed any modulation function in accordance with known modulation techniques. To incorporate these techniques in the heat flow calorimeter according to the present invention, the controller comprises a programmer for controlling the amount of heating by said heat source in accordance with a desired temperature value as a function of time.
The temperature value resulting from the control of the heat source by the controller may be selected to be a temperature value of the heat source itself. This may be attained by establishing a direct control loop between a temperature sensor in the heat source and an actual value input terminal of the controller while the desired temperature value is applied by the programmer to a set value input terminal of the controller.
Alternatively, in accordance with another preferred embodiment of the present invention, the desired temperature value as a function of time is a temperature at said sample position when a sample is not located at said sample position, said contr
Hütter Thomas
Jörimann Urs
Friedrich Kueffner
Hirshfeld Andrew H.
Mettler-Toledo GmbH
Verbitsky Gail
LandOfFree
Single cell calorimeter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Single cell calorimeter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Single cell calorimeter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2616329