We have compared the readings from a set of 30 RTD sensors read by a Hewlett-Packard controller and a set of 20 LM35 sensors read by Galil controllers. Assuming that the average of the RTD readings are equal to temperature in oC, we establish linear relationships between the Galil readings and temperature.

The requirements for DEIMOS call for an accuracy of better than ±0.5 oC for the RTD/H-P sensors and better than ±2 oC for the LM35/Galil sensors.

 The analysis here follows those of a similar measurement series and analysis for the ESI temperature sensors (Calibration of ESI Temperature Sensors, Burrous, Harper, and Mast, June 1998). The RTD/H-P sensors used here are identical to those used in the ESI series, and they will be used in DEIMOS. The LM35/Galil system used here is not the same as that used in the ESI measurements and will be used in DEIMOS.

 From the analysis of the RTD/H-P sensors in the ESI report we conclude that for the purposes of DEIMOS, we can simply use the RTD/H-P readings to be equal to temperature in centigrade. From the analysis below we conclude we can use a single linear conversion for all LM35/Galil readings to calculate temperature.

Temperature [oC] = 9.89 * reading - 1.08

 Readings were taken in environments spanning a temperature range form ~0 oC to ~20 oC. No absolute temperature reference was used, so we assume the average of thirty readings of the RTD / H-P system is equal to the temperature of the environment.

 The RTD sensors are held near each other in the air. The LM35 sensors are in air, soldered to a connector. We assume that thermal equilibrium is achieved for each test, and all sensors for each test were at the same temperature. We first describe the H-P system results and then the Galil system results.

RTD Sensors / H-P Controller

 An array of thirty RTD sensors (R.T.D. Company, RS2P-463) were held in air separated by ~ 3/8 inches using holes in a sheet (~ 1/8 inch) of fiberglass. The sensors were read using a Hewlett-Packard controller (Hewlett-Packard, HP34970A Data Acquisition / Switch, with three HP34901A 20-channel Armature Multiplexer cards, 10 sensors per card).

 The results are given in Spreadsheet No. 1. Configuration changes were only made to the LM35 / Galil system, and none were made to the RTD/H-P system.

If we assume the air temperature (oC) equals the average of the 26 sensor readings, then the sensor-to-sensor ms variation is ~0.1 oC to ~0.3 oC. Fitting the readings for each sensor to a linear relation between temperature and reading yields rms residuals of about 0.06 oC. This is about ten times that found in the ESI measurement series, where the sensors were inserted into blind holes an aluminum block. We ascribe the larger rms found here to real sensor-to-sensor temperature variations due to poorer thermal coupling in air.

Conclusion

Based on the measurements made in the ESI measurement series we concluded that the RTD/H-P sensors readily meet the DEIMOS requirements, and we recommend that the reading be used directly as temperature. This will save the efforts of any further calibration, bookkeeping, and software.

 LM35 Sensors / Galil Controller

 Eight LM35 sensors (National Semiconductor LM35 CZ/54AV) are soldered to each connector. Connectors A, B, C were used on analog boards #1, #2,#3 (24-bit analog input card, EL1230). Three Galil controllers (Galil DMC-1580, controller #0 S/N KK1611, controller #1 S/N KK0386, controller #2 S/N KK5106) were used to read the sensors. The test configurations are given in the table below. The configurations are listed in chronological order of data collection. The temperature of each test is given in the last column where the temperatures were determined from the average of the thirty RTD / H-P sensors.

Controller board test H-P temp (oC)

Boards 1,2, and 3 will be used with controllers 0, 1, and 2 respectively. Board #6 is a spare and was tested with all three controllers.

The sensor readings and analysis are given in Spreadsheet No. 2.

For each sensor we have calculated a slope and intercept in the relation

temperature(isensor,board,controller) = slope(isensor,board,controller) * reading(isensor,board,controller) + intercept(isensor,board,controller)

The intercept and slopes are given in Spreadsheet #2.

At the bottom of spreadsheet No. 2, we calculate the effect of using the average slope and intercept to convert all readings to temperature.

Temperature(isensor,board,controller) [oC] = 9.8922 * reading(isensor,board,controller) - 1.0839

The error made by this approximation has a range of order of ± 1oC. Since this is adequate for our goals for DEIMOS, we recommend using this equation. This saves the efforts of any further calibrations, bookkeeping, and software.