Lake Shore 321-01 User Manual
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Lake Shore Model 321 Autotuning Temperature Controller User’s Manual2-4 Installation2.7 SENSOR INSTALLATIONAbbreviated sensor installation recommendations for the Model 321 are included in this paragraph.Please refer to the Lake Shore Product Catalog or Sensor Guide for installation details and sensorspecifications. Call Lake Shore for copies of application notes or with questions or commentsconcerning sensor installation. The following are general recommendations on sensor installation:1. Do not ground the sensor.2. Shield the leads and connect the shield wire to SHIELD on the screw terminal connector only.Do not connect shield at the other end of the cable.3. Keep leads as short as possible.4. Use twisted-pair wire. Use of Lake Shore Duo-Twist™ wire (or equivalent) for two-wire, or Quad-Twist™ wire (or equivalent) for four-wire applications, is strongly recommended.5. Lead wires should be thermally anchored.Sensor installation is provided in two parts. Diode (Model 321-01) and Platinum (Model 321-02) sensorconnections are detailed in Paragraph 2.7.1. Thermocouple (Model 321-04) sensor connections aredetailed in Paragraph 2.7.2. Finally, sensor input error messages are described in Paragraph 2.7.3.2.7.1 Diode (Model 321-01) and Platinum (Model 321-02) ConnectionsThe Model 321 has a rear panel 6-pin input connector for silicon diode (Model 321-01) or platinumresistance (Model 321-02) sensors. The lead connections are defined in Table 2-1.Table 2-1. Diode or Platinum Input ConnectionsTerminal Description123456– Current– Voltage+ Current 500 μA (platinum)+ Voltage+ Current 10 μA (diodes)ShieldParagraph 2.7.1.1 discusses two-lead versus four-lead measurements. Paragraph 2.7.1.2 discussesconnecting leads. Sensor mounting is covered in Paragraph 2.7.1.3. Finally, Paragraph 2.7.1.4describes the effect of measurement errors due to AC noise.2.7.1.1 Two-Lead Versus Four-Lead MeasurementsThe use of a four-lead connection is highly recommended for two lead resistive elements anddiodes to avoid introducing current/resistive (IR) drops in the voltage sensing pair which translatesinto a temperature measurement error. In the two lead measurement scheme, the leads used tomeasure the sensor voltage are also the current carrying leads. The resultant voltage measured atthe instrument is the sum of the temperature sensor voltage and the IR voltage drop within the twocurrent leads. Since in a cryogenic environment, the flow of heat down the leads can be of criticalconcern, normally wire of small diameter and significant resistance per foot is preferred to minimizethis heat flow. Consequently, a voltage drop within the leads can be present.1. Two-Lead MeasurementsSometimes system constraints dictate the use of two-lead measurements. Connect the positiveterminals (V+ and I+) together and the negative terminals (V– and I–) together at theinstrument, then run two leads to the sensor.1-12-23' $ ! |
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