Lake Shore 321-01 User Manual
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Lake Shore Model 321 Autotuning Temperature Controller User’s Manual2-10 Installation2.9 PRECISION CALIBRATION OPTIONThe Precision Calibration Option is the easiest way to combine the additional performance of a LakeShore calibrated sensor with the Model 321 Temperature Transmitter. The Precision Calibration Optionis a read-only memory chip (PROM) with specific sensor calibration stored on it. The PrecisionCalibration Option improves combined sensor/instrument accuracy to within ±0.25 K or better over thecalibrated temperature range of the sensor.There are three types of precision options available for the Model 321. The Model 8000 PrecisionCalibration Option generates the data table from a Lake Shore calibrated sensor. The maximumnumber of data points is 99. A typical calibration precision option ranges between 30 and 40 pointsdepending on the sensor type and temperature range of the calibration. The data and accuracy of the fitis supplied to the user as a separate document. This information can be entered by the user over theserial interface.Prior to shipment, Lake Shore can also generate a custom sensor response curve from the individualsensor calibration as indicated in the above paragraph and store it in the Model 321 via the Model 8001Precision Calibration Option. The data and accuracy of the fit is then supplied to the user as asupplement to this manual.The Model 8002 Precision Calibration Option is used when the customer already owns a Model 321and wants the additional sensor calibration stored in the instrument. Lake Shore stores the calibrationdata in a NOVRAM and sends the programmed IC to the customer. The IC is then installed in theinstrument by the customer. The user should be prepared to supply the Model 321 serial number at thetime of order.The 8001-321 Precision Calibration Option is installed at Lake Shore when you order your instrumentwith a calibrated sensor. If you order the instrument to be used with a Lake Shore calibrated sensor thatyou already own, Lake Shore will need to know the model number and serial number of your sensor atthe time of order. The Model 8002-321 is for field installations of the Precision Calibration Option in anexisting Model 321.2.10 HEATER SETUPThe heater output of the Model 321 is brought out the back panel as a Dual Banana Jack. A matingconnector is supplied. Current is driven from the HEATER (HI) connection to the HEATER (LO)connection. A resistive heater load of 25Ω, 25 W should be connected between these two points.The heater output is a 1 A on High range, 0.31 A on Low range, and does not have to be fused. TheModel 321 is designed to power a 25 Ω heater for maximum heater output. A larger heater resistancemay also be used but will result in a lower maximum power output. For example, the output compliancevoltage is 25 volts so that a 100 Ω heater resistance allows a maximum power output of 6.25 watts[(25V) 2/100 Ω].If the heater load drops below ≈21 Ω, the output current will limit to prevent the instrument fromoverheating. The maximum output current will drop with the heater resistance when the resistance isbelow 21 Ω. The heater output is isolated from earth ground. To prevent heater noise coupling into themeasurement, do not allow the heater output to contact earth ground. For example, if the heater load is20 Ω, the maximum output current is ≈0.90 A. If the heater output is shorted, the maximum outputcurrent is ≈0.30 A.NOTE: The front panel Heater % display is calculated, not measured. If heater resistance is not 25 Ω,the display may not indicate actual heater output.NOTE: The heater output is isolated from earth ground. To prevent heater noise coupling into themeasurement, do not allow the heater output to contact earth ground. Earth ground is providedon the back panel for shielding purposes only.NOTE: If the heater leads must be close to the sensor leads, wind (twist) them in such a manner thatthey cross each other at ninety degrees. |
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