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USER'S MANUAL
Model DRC-91 C
Tem per at
u re Con
t ro I ler
Obsolete Notice:
This manual describes an obsolete Lake Shore product This manual is a copy from our archives
and may not exactly match your instrument Lake Shore assumes no responsibility for this
manual matching your exact hardware revision or operational procedures. Lake Shore is not
responsible for any repairs made to the instrument based on information from this manual.
Lakeshore.
Lake Shore Cryotronics, Inc.
575 McCorkle Blvd.
Westerville, Ohio 43082-8888 USA
Internet Addresses.
sales@ lakeshore com
service@ lakeshore com
Fax (614) 891-1392
Telephone (614) 891-2243
Methods
and apparatus disclosed
and
described herein have been developed solely on
company
funds
of Lake Shore
Cryotronlcs Inc
No
government or other contractual support
Or
relationship whatsoever has existed which
in
any way affects
or
mitigates proprietary rights of
Lake
Shore Cryotronlcs Inc in these developments
Methods
and apparatus disclosed
herein may be subject to U S Patents existing
or
applied
lor Lake
Shore Cryotronics Inc reserves the right to add
improve
modify or withdraw functions deslgn modifications or
poducts at any time without notice
Lake
Shore
shall
not be liable
lor
errors contained herein
or
lor incidental or consequential damages in connection wth furnishing performance
Or
use
of
this material
Manual No MAN-DRC-91 C
December, 1987
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Summary of Contents for Lakeshore DRC-91 C
- Page 176 Lake Shore Cryotronics, Inc. APPLICATION NOTES This appendix includes the following Lake Shore documentation: 1. Fundamentals For Usage Of Cryogenic Temperature Controllers – Application Note .....Page 1 2. Standard Curve 10 – Technical Data ....................Page 8 3. DT-470 Series Temperature Sensors Installation and Operation – Application Note.....Page 10 4.
- Page 177 Lake Shore Cryotronics, Inc. III PROPORTIONAL CONTROL The block diagram in Figure 1 shows a systems in which only proportional control is being used. In this system, the desired control temperature setting (set point) is being compared to the sensor signal and the difference, or error signal (including polarity), is amplified within the controller.
- Page 178 Lake Shore Cryotronics, Inc. To illustrate the effect of the sensor, in more detail, consider the idealized curve (Figure 4) for a Lake Shore silicon diode which has a nominal sensitivity of -50 mV/K below 30 kelvin and -2.5 mV/K above 30 kelvin. Figure 3 illustrates the effect of converting the voltage error signal (horizontal axis) to its equivalent temperature error for the two sensitivity regions of the silicon diode sensor.
- Page 179 Lake Shore Cryotronics, Inc. Since the thermal conductivity of cryogenic materials is finite, good practice dictates that the controller power output be the same order of magnitude as the cooling power. If, for example, the cooling power is 0.2 watt, and 50 watts is available, a change in set point to a higher temperature outside the proportional band of the controller will dump 50 watts into the system block.
- Page 180 Lake Shore Cryotronics, Inc. The Real World Revisited Since a real cryogenic system has non-zero thermal resistance, the value of the reset is important in setup of the controller. The amount of reset desired is dependent on: (1) the time required for the control sensor to reach equilibrium once it enters the proportional band;...
- Page 181 Lake Shore Cryotronics, Inc. VI SENSOR CONSIDERATIONS Sensor Gain Revisited: Since a controller will amplify input noise as well as sensor signal, it becomes important to consider sensor performance when designing a complete system. The Lake Shore DT-500 Series Sensors have a voltage-temperature characteristic which lend themselves to cryogenic temperature control use because of their high sensitivity at low temperatures (Figure 3).
- Page 182 Lake Shore Cryotronics, Inc. For Further Reading E. M. Forgan, "On the Use of Temperature Controllers in Cryogenics". Cryogenics 14 (1974), pp. 207-214. This is a cogent discussion of the interaction between the electrical and thermal response times in a typical cryogenic control system.
- Page 183 Lake Shore Cryotronics, Inc. Standard Curve 10 Standard Curve 10: Measurement Current = 10 µA ±0.05% dV/dT dV/dT dV/dT T (K) Voltage T (K) Voltage T (K) Voltage (mV/K) (mV/K) (mV/K) 1.40 1.69812 –13.1 16.0 1.28527 –18.6 95.0 0.98564 –2.02 1.60 1.69521 –15.9...
- Page 184 Lake Shore Cryotronics, Inc. POLYNOMIAL REPRESENTATION Curve 10 can be expressed by a polynomial equation based on the Chebychev polynomials. Four separate ranges are required to accurately describe the curve. Table 1 lists the parameters for these ranges. The polynomials represent Curve 10 on the preceding page with RMS deviations of 10 mK.
- Page 185 Lake Shore Cryotronics, Inc. DT-470 SERIES TEMPERATURE SENSORS INSTALLATION AND OPERATION There are three aspects of using a temperature sensor which are critical to its optimum performance. The first involves the proper electrical and thermal installation of the connecting leads which run to the sensor, while the second aspect is the actual mounting of the sensor to the sample assembly.
- Page 186 Lake Shore Cryotronics, Inc. DT-470-SD The SD version is the basic package for the DT-470 sensor line from which all other configurations are made using the appropriate adapter. The base of the device has a gold metallized surface and is the largest flat surface on the sensor.
- Page 187 Lake Shore Cryotronics, Inc. DT-470-ET / DT-470-MT DT-470-ET DT-470-MT Both adapters are gold-plated copper hex head bolts with the SD package mounted in a slot on the adapter head. The ET adapter screws into a ¼ inch deep, 6-32 threaded hole while the MT adapter screws into a 6 mm deep, 3x0.5 mm threaded hole.
- Page 188 Lake Shore Cryotronics, Inc. FIGURE 1. Four-Wire Configuration for DT-470 Installation SENSOR OPERATION Temperature controllers and thermometer instrumentation manufactured by Lake Shore Cryotronics are designed to be directly compatible with the DT-470 sensor to give optimum performance and accuracy together with direct temperature readouts.
- Page 189 Lake Shore Cryotronics, Inc. MEASUREMENT SYSTEM INDUCED ERRORS IN DIODE THERMOMETRY by John K. Krause and Brad C. Dodrill Diode temperature sensors are capable of being used at the accuracy level of a few hundredths of a kelvin. However, in order to achieve this performance, proper measurement techniques must be used.
- Page 190 Lake Shore Cryotronics, Inc. There are two simple techniques which can be used to test whether these errors might be present in a measuring system. The first is to connect a capacitor (about 10 µF) in parallel with the diode to act as a shunt for any ac noise currents.
- Page 191 Lake Shore Cryotronics, Inc. This stability gives a deceptive view of exactly how accurate the temperature measurement really is and emphasizes the importance of checking all aspects of a measuring system. The measured offset voltages shown in Figs. 4 and 6 can be understood by using the well-known result from p-n junction theory: I = I [exp(eV / nkT) - 1]...
- Page 192 Lake Shore Cryotronics, Inc. The utilization of the small signal model has the advantage of being analytically simple. However, the model does not contain the nonlinearity inherent in the forward biased IV characteristics of a p-n junction. In an cos ω t) was attempt to retain the non linear characteristics, V(I expanded in a Fourier series.
- Page 193 Lake Shore Cryotronics, Inc. IV. CONCLUDING REMARKS Noise in any measurement circuit is undesirable and should be eliminated to as great an extent as possible. The first step is to electrically shield all instrumentation and wiring and use proper grounding techniques. Secondly, the diode measurement circuit should have a single circuit ground which is generally made at the voltmeter and which then requires a floating current source.
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