805 Lake Shore Cryotronics Temperature Controller

The Lake Shore Cryotronics 805 Temperature Controller is a microprocessor based instrument which provides true analog control. It accepts inputs from up to two sensors and displays the temperature with up to (4) digits of solution in K, °C, or °F. It displays voltage for diodes to 1 millivolt, and ohms for resistors to four places.

The dual sensor input allows the user to monitor temperature at more than one point. Sensor select pushbuttons on the front panel enable the user to display either input at will. The system control sensor is selected via a rear-panel toggle switch with the choice indicated on the front panel. This choice is independent of display status.

The Lake Shore Cryotronics 805 Temperature Controller is direct reading in temperature when used with the Lake Shore Cryotronics DT-470 Series Temperature Sensors. All DT-470 Sensors follow the same temperature response curve. Four bands of tracking accuracy are offered so that sensor selection may be made with both technical and economical considerations for any given applications. Low temperature (2 to 100K) accuracies range from 0.25K for band 11 to 1K for band 13. For more demanding requirements, DT-470 Sensors can be individually calibrated to accuracies of better than 50 millikelvin depending on temperature range.

Diode sensor voltages are digitized with a resolution of 100 microvolts out of 3 volts full scale. For the display, temperature is rounded to 0.1 kelvin above 100 kelvin, and to 0.01 kelvin below 100 kelvin.

For greater precision individual sensor calibrations can be accommodated through the 8001 Precision Calibration Option which programs the instrument with a particular response curve. The algorithm within the instrument interpolates between data points to an interpolation accuracy which exceeds 0.01K over the entire temperature range of the Precision Option. The analog-to-digital converter is accurate to plus or minus the least significant bit, which for the 470 series sensor results in an uncertainty of 1mK below 28K and 45mK above 40K with a transitional region between the two temperatures. Therefore, at temperatures below 28K, the overall system accuracy, the sum of the instrument accuracy (11mK) and that of the calibration itself (Lake Shore calibrations are typically better than 20mK within this region) is ±0.03K. Above 28K, system accuracy gradually moderates to a typical value of ±75mK above 40K.

The Lake Shore Cryotronics 805 Temperature Controller's display uses digital filtering which averages up to ten temperature readings. This reading mode eliminates noise within the cryogenic system analogous to averaging with a digital voltmeter. This algorithm can be deselected (bypassed) by switch 2 of the SENSOR ID dip switch on the back panel for a given input if the user prefers not to average readings. A decimal point at the upper left of the display indicates that averaging is on.

The Lake Shore Cryotronics 805 Temperature Controller can also be used with the optional input conversion modules (-6) which allow either input to be converted to handle either the Lake Shore Cryotronics TG-120 series diodes (or any diode with a 0 to 6 volt output), or positive temperature coefficient metallic resistors., i.e., platinum (-P2 or -P3) or rhodium-iron (-R1) resistors. The DIN curve is standard within the instrument and is called up automatically unless a precision option is present for the platinum resistor. The accuracy of the reading is dictated by the sensor and its conformity to the DIN curve. The tolerance on these devices is given on the technical data sheet for the Lake Shore Cryotronics PT100 series sensors. The combined accuracy of the instrument and a calibrated resistor with a precision option is on the order of 40mK over the useful range of the sensor (above 40K for the platinum). Note that a precision option is required for a rhodium-iron or a TG-120 to read correctly in temperature.

These input conversion modules are easily installed by the user; thus, 1-2 units can be modified to satisfy changing requirements.

The ample memory space provided in the 805 allows several response curves to be stored in one instrument. Depending on the complexity of the curves, up to ten can be programmed into the unit by Lake Shore. The SENSOR ID switches are used to select which particular sensor response curve is to be used with each input. Thus, the user is able to make sensor changes at will even when different response curves are required.

The data for calibrated sensors can be stored within the instrument by means of the 8001 Precision option. Each curve can contain up to 99 sensor unit-temperature data points. With the standard precision option format, which consists of 31 data points and a 20 character information line, up to ten curves can be stored in the unit.

Although voltage (resistance)- temperature data points are stored as a table, interpolation within the instrument results in the equivalent of a high order polynomial calculation in the converting of the input voltage (or resistance) to temperature. This is done by means of a proprietary algorithm developed at Lake Shore Cryotronics.

The control temperature set-point selection is made via thumbwheel switches on the front panel of the instrument. The set-point switches, which provide a continuous indication of the set-point value, enable the user to quickly and easily determine whether his system is at control temperature. The set-point is in the same units as is the Display sensor (kelvin, Celsius, fahrenheit, or volts [ohms]).

The control section of the 805 provides two-term temperature control. Proportional (GAIN) and integral (RESET) are individually tuned via front-panel potentiometers. The gain and reset settings are in nominal log per cent.

Analog heater output of the Lake Shore Cryotronics 805 Temperature Controller is a maximum of 25 watts when a 25 ohm heater is used. A digital meter on the front panel of the 805 continuously shows the heater power output as a percentage of output range. Thus, the user can conveniently monitor power applied to his system. To accommodate systems which require lower heater power, the maximum heater output of the 805 can be attenuated in two steps of a decade each. When greater power output is required, an optional 60 watt power output stage has been manufactured (W60) which is designed for a 25 ohm load. It is rated at a nominal 1.5 amperes with a compliance of 43 volts.

An optional IEEE-488 (Model 8054) or RS-232C (Model 8053) interface have been manufactured for the 805. Either interface can be used to remotely control all front-panel functions.