Lake Shore 321-01 User Manual
                                                                                                                                  | |
Contents
| 
Lake Shore Model 321 Autotuning Temperature Controller User’s ManualInstallation 2-5Some loss in accuracy can be expected since the voltage measured at the voltmeter becomesthe sum of the sensor voltage and the voltage drop across the connecting leads. The exactmeasurement error will depend on sensor sensitivity and variations resulting from changingtemperature. For example, a 10 Ω lead resistance will result in a 0.1 mV voltage error. Theresultant temperature error at liquid helium temperature is only 3 mK, but, because of thediode’s lower sensitivity (dV/dT) at higher temperatures, it becomes 10 mK at liquid nitrogentemperature.2. Four-Lead MeasurementsAll sensors, including both two-lead and four-lead devices, can be measured in a four-leadconfiguration to eliminate the effects of lead resistance. The exact point at which the connectingleads are soldered to the two-lead sensor normally results in a negligible temperatureuncertainty.I+V+I–V–Four-LeadDiodeFour-LeadPlatinumI+V+I–V–The four-lead measurement configuration should always be used with Series PT-100 PlatinumSensors being attached to the Model 321-02.2.7.1.2 Connecting Leads To The SensorAn excessive heat flow through the connecting leads to any temperature sensor can create asituation where the active sensing element is at a different temperature than the sample to whichthe sensor is mounted. This is then reflected as a real temperature offset between what ismeasured and the true sample temperature. Such temperature errors can be eliminated by properselection and installation of the connecting leads.In order to minimize any heat flow through the leads, the leads should be of small diameter and lowthermal conductivity. Phosphor-bronze or Manganin wire is commonly used in sizes 32 or 36 AWG.These wires have a fairly low thermal conductivity yet the electrical resistivities are not so large asto create any problems in measurements.Lead wires should also be thermally anchored at several temperatures between room temperatureand cryogenic temperatures to guarantee that heat is not being conducted through the leads to thesensor.2.7.1.3 Sensor MountingBefore installing a diode sensor, identify which lead is the anode and which is the cathode. Whenviewed with the base down and with the leads towards the observer, the positive lead (anode) is onthe right and the negative lead (cathode) is on the left. The Lake Shore DT-470-SD silicon diodesensor lead configuration is shown below. For other sensors, read the accompanying literature orconsult the manufacturer to ensure positive identification of sensor leads. Be sure the leadidentification remains clear even after installation of the sensor. It is also a good idea to record theserial number and location of the sensor.DT-470-SDDiode Sensor LeadsAnodeCathode |
Related manuals for Lake Shore 321-01
manualsdatabase
Your AI-powered manual search engine