- Email: [email protected]
Operation of the TVO temperature sensors in the range from 4.2 K up to 425 K
Cryogenics 44 (2004) 735–739 www.elsevier.com/locate/cryogenics
Operation of the TVO temperature sensors in the range from 4.2 K up to 425 K Y.P. Filippov *, T.I. Smirnova Laboratory of Particle Physics, Joint Institute for Nuclear Research, Dubna 141980, Moscow Region, Russian Federation Received 10 September 2003; received in revised form 20 January 2004; accepted 13 April 2004
Abstract The report continues our investigations on cryogenic thermometers. To estimate the influence of warming the well known TVO temperature sensors [Proceedings of the ICEC17 (1998) 699, Cryogenics 41 (2001) 213, Advances in Cryogenic Engineering 45B (2000) 1817, Proceedings of the ICEC18 (2000) 627] up to 425 K on their calibration curve, a series of experiments have been carried out. The number of thermal cycles in the range from 425 K down to 77.3 K was 105. Comparison of readings of the sensors at 293, 77.3 and 4.2 K was performed with initial calibration curves for 100 cycles. Then several sensors were re-calibrated, and a new comparison was done during five additional thermal cycles at the same temperatures. The obtained results are discussed and they seem to be optimistic. 2004 Elsevier Ltd. All rights reserved. Keywords: Temperature sensor; Thermal cycling; Instrumentation
1. Introduction Some devices of modern physics installations have to operate under conditions combining vacuum environment, cryogenic and relatively high temperatures. An example is a cryogenic panel of a vacuum pump which should be periodically warmed up to 150 C (423 K) after operation at 4.2 K. Typical conditions for them can be as follows: operation during a day at 4.2 K with subsequent regeneration at nitrogen temperatures (about 80 K). Weekly regeneration at 300 K and monthly regeneration at 423 K has to be done as well. If the service life is estimated as approximately 10 years, the total number of warmings up to 423 K could be about 100 or more. It is known, in particular, that temperature sensors based on a TVO resistor [1–4] can operate successfully at 1.5 K
*
Corresponding author. Tel.: +7-09621-65-813; fax: +7-0962165767. E-mail address: yury.fi[email protected] (Y.P. Filippov). 0011-2275/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.cryogenics.2004.04.002
approximately and instant cooling down to 77.3 K for 100 cycles.
2. Methods and experimental set-up The detailed characteristics of all the tested sensors are presented in [1–4]. A schematic of the experiment is shown in Fig. 1. First of all, a batch of TVO resistors was treated with 25 time thermal cycling between 373 and 77.3 K––procedure 1, and sensors showed the smallest deviation at 77.3 K were preliminary chosen. Then these sensors were calibrated between 3.0 and 293 K––procedure 2. To calibrate the sensors, we have used system AK-6.30 [5]. The temperature of the comparison block with calibrated sensors is measured by the reference Rhodium-iron resistive thermometer RIRT-1 [4]: its accuracy is of ±1 mK for all the range. After this, preliminary measurements were done at 293, 77.3 (liquid nitrogen) and 4.2 K (liquid helium), and seven sensors were selected for thermal cycling––procedures 3 and 4. The selection criteria is that the maximum relative temperature deviations DT =T at 77.3 and 4.2 K should be within ±0.25%, i.e. ±10 mK at 4 K. For example, the TVO sensors with DT =T -values of ±0.25%, )0.16% and )0.05% at 4.2 K were selected for tests. Such instability
736
Y.P. Filippov, T.I. Smirnova / Cryogenics 44 (2004) 735–739 Calibration in the range from 3.0 K to 293 K at 32 points
Thermal cycling from 373 K to 77.3 K 25 times
Preliminary measurements at
2
293 K, 77.3 K and 4.2 K
3
Selection of the sensors
1
4
Post thermal cycling measurements at 293 K, 77.3 K and 4.2 K
Thermal cycling from 425 K to 77.3 K
Re-calibration and comparison with initial calibration
6
5
7
Short-term additional thermal cycling from 425 K to 77.3 K
8
Fig. 1. A schematic of the experiment.
of the TVO sensors can be caused by individual features of the TVO resistors and also with different conditions during calibration and measurements. Thus, the calibration is carried out with thermally conductive silicon grease between sensors and a copper comparison block in vacuum, and a temperature rate during cooling down to 4.2 K is rather low––about 0.001 K/s. Conversely, the test measurements are done with liquid nitrogen or liquid helium around the sensors at atmospheric pressure, and the temperature rate while cooling down to 4.2 K is rather fast––about 50 K/s. Then a series of experiments was carried out with thermal cycling of the selected sensors between 425 and 77.3 K (liquid nitrogen)––procedure 5. There were two possibilities to warm up the sensors in a furnace: vacuum environment and with hot air. The second way was chosen to provide harder conditions (presence of oxygen) with respect to a real case when warming up can be performed in vacuum. The temperature in the furnace with hot air was regulated with deviation of ±2 K around 423 K (150 C), so the maximum temperature was 425 K. The exposition time at this temperature was about 1 h for the first 50 cycles and 10 min for the rest 50 cycles. A comparison of the readings of the sensors with initial calibration curves––procedure 6––was performed at room temperature, in liquid nitrogen and liquid helium about 20 h after thermal cycling. From time to time, additional measurements at the same temperatures were also done in a day, in a week and in a month: it was done after the 10th, 15th, 20th and 25th cycles. We kept the sensors at room temperature between additional measurements. After 100th cycle, additional measurements were done in 1 week and then in every month. The measurements of TVO resistances were made by means of a new temperature monitor of our own production. This is a box of 180 · 76 · 24 mm3 connected to COM-port (RS232) of a personal computer. A four-lead technique is used to measure the resistance of the temperature sensor with respect to the precision reference resistor. To avoid the influence of parasitic voltages,
measurements are performed with a direct current source whose polarity can be changed. The main characteristics of the temperature monitor are as follows: the number of measured channels/sensors can be from 1 up to 15; the range of measuring current is from 0.5 lA to 5 mA; the range of measured resistances, R, is from 1 X to 100 kX; the accuracy of measurements is DR=R 6 0:01%; the time to measure all the channels is about 1.6 s; the sensors are connected in series. A mercury (Hg) thermometer of ±0.1 K accuracy was used to measure the reference value at room temperature. Our preliminary experiments have shown that differences between readings of RIRT-1 and the temperatures of saturation in liquid nitrogen (LN2 ) and liquid helium (LHe) were ±0.03 and ±0.002 K, correspondingly. Inasmuch as these values are significantly less than the possible instability of the TVOresistors, the temperatures of saturation Ts have been used as the reference values while measuring in LN2 and LHe. Corresponding depths of immersion of the sensors to dewars were the same during all the measurements. Since the initial deviations of the tested TVO-sensors are different, it would be useful to determine a zero point for all the sensors in order to present the results for comparison. To do this, the following procedure was used. The initial readings of all the tested sensors before warming up to 425 K (procedure 3) were measured at T 293 K (ambient air), Ts 77:3 K and Ts 4:2 K, and the values of dT0 ¼ TTVO Ts (or TTVO THg ) for each sensor were calculated, where TTVO and THg are temperatures of the TVO sensor and the mercury thermometer, respectively. After thermal cycling (procedure 6) the corresponding readings dT1 ¼ TTVO Ts were found, and the results were presented as DT ¼ dT1 dT0 versus N where N is a number of thermal cycles. The readings of the carbon–glass temperature sensor CRT-2 [4], calibrated 5 years ago, were used as additional reference while measuring in LN2 and LHe after the 10th cycle: DTCRT ¼ dTCRT dTs , where TCRT is calculated by means of its calibration polynomial. This reference sensor was not treated with thermal cycling. Its instability is estimated as DT =T 6 0:15%.
Y.P. Filippov, T.I. Smirnova / Cryogenics 44 (2004) 735–739 1 0.5 0
∆T , K
Finally, four chosen sensors were re-calibrated and a full-scale comparison with initial calibration curves was carried out––procedure 7. Afterwards, an additional thermal cycling––procedure 8––was done for the recalibrated sensors, and again the comparison with new calibration curves was carried out.
737
0
1
2
3
4
5
-0.5
6
7
8
9
1 0
1 1
1 2
1 3
1 4
1 5
1 6
1 7
1 8
1 9
2 0
2 1
2 2
2 3
2 4
2 5
2 6
2 7
2 8
2 9
293 K
-1 -1.5 -2
3. Results and discussions
CRT 449
2916 458
3215 459
354 4515
-2.5
1 2 3 4 5 6 7 8 9 10 13 15 16 18 20 21 23 25 N 1d 1w 1m 2w 1m 1d 1w 1m 1d 1w 1m
0.2
3.1. 100-time thermal cycling
0.1 0 -0.1
∆T , K
-0.2 -0.3 -0.4 -0.5
77.3 K
-0.6 -0.7
CRT 354 459
-0.8
2916 449 4515
3215 458
-0.9 5
0
CRT 354 459 0
1
2
3
4
5
6
7
8
9
10
1
1
12
1
3
1
4
1 5
1
6
1
7
1 8
1 9
2916 449 4515 20
2
1
2
2
23
3215 458 2
4
2
5
26
2
7
2 8
-5
∆T , mK
At the beginning, three sensors (#2916, #3215 and #354) were tested during 10 cycles. Then the second group of four sensors (#449, #458, #459 #4515) was tested separately also during 10 cycles. Immersions in liquid helium were not always made: the corresponding points are absent in the plot in this case. Afterwards these seven sensors were tested together up to 100 cycles. The results for the first 25 cycles, corresponding to procedure 6 in Fig. 1, are given in Fig. 2. Noteworthy is that temperature shifts of more than )2 K at 293 K, )0.5 K at 77.3 K and )20 mK at 4.2 K appear for sensor #354 right after the first thermal cycle. During 10 cycles, one can observe a tendency of DT to grow for rest of the sensors mainly within (0–0.5 K) at 293 K and to decrease within (0.1 to )0.3 K) at 77.3 K and (0 to )10 mK) at 4.2 K. A post-thermal cycling period (marked as 1d, 1w and 1m in Fig. 2) leads to reduction of DT at 293 K by 0.4 K approximately although the values of DT remain almost the same at 77.3 K, and one can see some DT -values decreasing at 4.2 K. The next noticeable result was observed for sensor #459 after the 16th cycle: DT became about )1.0 K at 293 K, )0.7 K at 77.3 K and )19 mK at 4.2 K. This sensor showed a maximum shift of )1.66 K at 293 K and )22 mK at 4.2 K a week after the 20th cycle. In its turn, the shifts for sensor #354 became closer to the DT values for rest of the five sensors after the 16th cycle. Except sensor #459, the shifts for six sensors decreased down to (0.1 to )0.7 K) at 293 K, ()0.1 to )0.35 K) at 77.3 K and ()5 to )11 mK) at 4.2 K after the 25th cycle. As for sensor #459, its DT values became about )1.4 K at 293 K, )0.8 K at 77.3 K and )23 mK at 4.2 K after the 25th cycle, i.e. 1 month after this cycle. As it was expected, the readings of CRT-2 remained approximately the same during all the experiment. One can note that the time to complete this part of the experiment required about 6 months. The results of further thermal cycling are shown in Fig. 3. One can see that the temperature shifts were relatively stable for all the sensors at all the temperatures after the 25th cycle including the 100th cycle and the three-month period after thermal cycling. The differences in the shifts for TVO sensors remained approximately the same, and insignificant deviations or
-10 -15 -20
4.2 K
-25
1 2 3 4 5 6 7 8 9 10 13 15 16 18 20 21 23 25 N 1d 1w 1m 2w 1m 1d 1w 1m 1d 1w 1m
Fig. 2. Temperature shifts DT versus the number of thermal cycling N and the additional period after thermal cycling––d (day), w (week), m (month): initial part.
oscillations of DT can be explained, in particular, by the errors of measurements and instability of the sensors. The time to complete thermal cycling from 30 to 100 and post-cycling measurements was about 6 months as well. So, the total experimental period was about 1 year. In addition, it is necessary to emphasize that no mechanical defects or cracks were revealed in the ceramic shell of the TVO resistors during all the experiment. In its turn, a common distinguishing feature appeared: the green color of all the sensor shells was becoming deeper tinged with brown due to oxidation at 425 K. However this does not matter for practical application. 3.2. Re-calibration Five months after completing the thermal cycling, four sensors––#2916, #354, #459 and #4515––were calibrated again, and the results of the comparison with the initial calibration curves are shown in Fig. 4. As it is seen, the best sensor #2916 has demonstrated a remarkable ability to reproduce the initial calibration
738
Y.P. Filippov, T.I. Smirnova / Cryogenics 44 (2004) 735–739 1 2916
3215
354
449
458
459
4515
0 .5
∆T , K
0 -0 .5
293 K
-1 -1 .5
25 1d 1w 1m
30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 N 1w 1m 2m 3m
0 -0.1
∆T , K
-0.2 -0.3 -0.4 -0.5 CRT
2916
3215
354
449
458
459
4515
-0.6 -0.7
77.3 K
-0.8 -0.9 0
to 70 K. As for the worst sensor #459, its maximum values of dT =T 1:3% were revealed near the temperature of 150 K, and dT =T were )0.6% at 3.0 and 4.2 K. Negative values of dT mean that the resistances of the sensors are increased due to some defects in the sensitive parts and perhaps in the contact parts caused by thermal cycling. One can note that a good agreement (dT =T < 0:1%) exists between the temperature shifts after procedure 6 of the whole procedure (Fig. 3) and re-calibration procedure 7 (Fig. 4) for sensors #459 and #4515 at 293, 77.3 and 4.2 K. As for sensors #2916 and #354, there is a good agreement for them at 293 K ()0.12 K against )0.16 K for #2916 and 0.48 K against 0.40 K for #354). However, deviations of about 0.15 K at 77.3 K and 6 mK at 4.2 K were found for these sensors. They can be explained as a result of different conditions during calibration and measurements and also with individual features of the TVO resistors commented above in item 2.
-5
∆T ,mK
3.3. Additional thermal cycling -1 0
4.2 K
-1 5 CRT
2916
3215
354
449
458
459
4515
-2 0
-2 5
25 1d 1w 1m
30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 N 1w 1m 2m 3m
Fig. 3. Temperature shifts DT versus the number of thermal cycling N and the additional period after thermal cycling––d (day), w (week), m (month): continuation.
0.2 0
It was interesting to estimate the behavior of the sensors after re-calibration: to make sure that the readings of the sensors remained stable and to demonstrate a final quality of the sensors. In principle, one can suppose that a qualitative picture could look like results around the 30th cycle. One can see that some growth of temperature shifts observed for the 30th cycle for 293, 77.3 and 4.2 K, and then the DT values may be approximately the same (Fig. 3). After re-calibration, an additional short-term thermal cycling between 425 and 77.3 K was carried out in two weeks. The results of measurements for the re-calibrated sensors are presented in Fig. 5 after the 1st (101st), 3d (103d) and 5th (105th) 0.4
-0.4 -0.6
∆T , K
δ T/ T, %
-0.2
2916
-0.8
35 4
-1
45 9 -1.2
0 -0.2
4515
101
-1.4
3
10
Temperature, K
100
300
Fig. 4. Comparison of the calibration curves: dT =T ¼ ðT1 T0 Þ=T , where subscripts 1 and 0 refer to new and initial calibrations.
105
1d
1w
∆T , mK
N 77.3 K
101
curve: its maximum deviation dT =T does not exceed )0.12% at 150 K that corresponds to dT ¼ 0:18 K. The temperature shifts of sensor #354 are not greater than )0.2% at 20 K although this sensor was showing the maximum temperature shifts DT during the first 10 cycles (Fig. 2). The typical sensor #4515 has shown shifts dT =T from )0.26% to )0.6% in a range from 4.2 to 70 K and from )0.036% to )0.6% in a range from 293
103
0.16 0.12 0.08 0.04 0 -0.04
∆T , K
1
293 K
0.2
103
105
1d
1w
N
5 3 1 -1
4.2 K
2916
354
459
4515
CRT
Fig. 5. Temperature shifts DT versus the number of thermal cycling N and the additional period after thermal cycling–– d (day), w (week).
Y.P. Filippov, T.I. Smirnova / Cryogenics 44 (2004) 735–739
additional cycles and after 1 day and 1 week. The results are presented as DT ¼ dT1 dT0 versus N (including CRT-2 sensor) that was commented above in item 2. As it is supposed, one can see a relatively small growth of DT for the 101th cycle at all the temperatures for all the sensors: up to 0.3 K at 293 K, 0.15 K at 77.3 K and 0.004 K at 4.2 K. For the 103th and 105th cycles, the temperature shifts remained the same in the limits of the accuracy of the measurements. One day and 1 week after thermal cycling, some expected decrease of DT by about 0.1 K at 293 K and 0.06 K at 77.3 K is observed. As for the temperature of 4.2 K, the temperature shifts for all the sensors are practically the same as during the thermal cycling. These results can be estimated as very good ones. In addition, one can note that the behavior of the former worst sensor #459 (see Fig. 4) looks approximately the same in Fig. 5 as for the best sensor #2916.
739
racy for the practical usage The structures of the sensitive parts/elements, and subsequently, the resistances of the sensors can change during the first twenty cycles. Afterwards the readings of the sensors remain stable: the corresponding deviations do not exceed the value of instability expected for the TVO-resistors. In order to use the TVO-sensors in the range from 4.2 to 425 K with relatively high accuracy––DT =T 6 0:25%, one needs to carry out 25 times thermal cycling between 425 and 77.3 K with subsequent calibration.
Acknowledgement Many thanks to our colleague V.M. Miklaeyv for his help to re-calibrate the temperature sensors.
References 4. Conclusions The influence of additional thermal cycling between 425 and 77.3 K on the readings of the TVO temperature sensors prepared in the usual way––preliminary thermal cycling from 373 to 77.3 K during 25 times, is as follows. There are two types of sensors: the majority (five of seven) for which the maximum temperature shifts DT =T are relatively small––down to )0.25% at 293 K, )0.5% at 77.3 K and )0.4% at 4.2 K, and the minority (two of seven) for which the values of DT =T can reach down to )0.7% at 293 K, )1.0% at 77.3 K and )0.6% at 4.2 K, approximately. These deviations can be considered as satisfactory accu-
[1] Suesser M. Characteristics of the TVO temperature sensors. In: Proceedings of the ICEC17, Bournemouth, UK, 1998, p. 699–702. [2] Suesser M, Wuechner F. Mechanical behavior of carbon ceramic TVO temperature sensors. Cryogenics 2001;41:213–5. [3] Balle C, Casas J, Rieubland JM, Suraci A, Togny F, Vauthier N. Influence of thermal cycling on cryogenic thermometers. In: Advance in cryogenic engineering, vol. 45B, Kluwer Academic/ Plenum Publisher, New York, Boston, Dordrecht, London, Moscow; 2000, p. 1817–23. [4] Dedikov YA, Filippov YP. Characteristics of Russian cryogenic temperature sensors. In: Proceedings of the ICEC18, Mumbai, India, 2000, p. 627–30. [5] Filippov YP, Kovrizhnykh AM, Miklayev VM, Sukhanova AK. Metrological systems for monitoring two-phase cryogenic flows. Cryogenics 2000;40:279–85.
Operation of the TVO temperature sensors in the range from 4.2 K up to 425 K Y.P. Filippov *, T.I. Smirnova Laboratory of Particle Physics, Joint Institute for Nuclear Research, Dubna 141980, Moscow Region, Russian Federation Received 10 September 2003; received in revised form 20 January 2004; accepted 13 April 2004
Abstract The report continues our investigations on cryogenic thermometers. To estimate the influence of warming the well known TVO temperature sensors [Proceedings of the ICEC17 (1998) 699, Cryogenics 41 (2001) 213, Advances in Cryogenic Engineering 45B (2000) 1817, Proceedings of the ICEC18 (2000) 627] up to 425 K on their calibration curve, a series of experiments have been carried out. The number of thermal cycles in the range from 425 K down to 77.3 K was 105. Comparison of readings of the sensors at 293, 77.3 and 4.2 K was performed with initial calibration curves for 100 cycles. Then several sensors were re-calibrated, and a new comparison was done during five additional thermal cycles at the same temperatures. The obtained results are discussed and they seem to be optimistic. 2004 Elsevier Ltd. All rights reserved. Keywords: Temperature sensor; Thermal cycling; Instrumentation
1. Introduction Some devices of modern physics installations have to operate under conditions combining vacuum environment, cryogenic and relatively high temperatures. An example is a cryogenic panel of a vacuum pump which should be periodically warmed up to 150 C (423 K) after operation at 4.2 K. Typical conditions for them can be as follows: operation during a day at 4.2 K with subsequent regeneration at nitrogen temperatures (about 80 K). Weekly regeneration at 300 K and monthly regeneration at 423 K has to be done as well. If the service life is estimated as approximately 10 years, the total number of warmings up to 423 K could be about 100 or more. It is known, in particular, that temperature sensors based on a TVO resistor [1–4] can operate successfully at 1.5 K
*
Corresponding author. Tel.: +7-09621-65-813; fax: +7-0962165767. E-mail address: yury.fi[email protected] (Y.P. Filippov). 0011-2275/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.cryogenics.2004.04.002
approximately and instant cooling down to 77.3 K for 100 cycles.
2. Methods and experimental set-up The detailed characteristics of all the tested sensors are presented in [1–4]. A schematic of the experiment is shown in Fig. 1. First of all, a batch of TVO resistors was treated with 25 time thermal cycling between 373 and 77.3 K––procedure 1, and sensors showed the smallest deviation at 77.3 K were preliminary chosen. Then these sensors were calibrated between 3.0 and 293 K––procedure 2. To calibrate the sensors, we have used system AK-6.30 [5]. The temperature of the comparison block with calibrated sensors is measured by the reference Rhodium-iron resistive thermometer RIRT-1 [4]: its accuracy is of ±1 mK for all the range. After this, preliminary measurements were done at 293, 77.3 (liquid nitrogen) and 4.2 K (liquid helium), and seven sensors were selected for thermal cycling––procedures 3 and 4. The selection criteria is that the maximum relative temperature deviations DT =T at 77.3 and 4.2 K should be within ±0.25%, i.e. ±10 mK at 4 K. For example, the TVO sensors with DT =T -values of ±0.25%, )0.16% and )0.05% at 4.2 K were selected for tests. Such instability
736
Y.P. Filippov, T.I. Smirnova / Cryogenics 44 (2004) 735–739 Calibration in the range from 3.0 K to 293 K at 32 points
Thermal cycling from 373 K to 77.3 K 25 times
Preliminary measurements at
2
293 K, 77.3 K and 4.2 K
3
Selection of the sensors
1
4
Post thermal cycling measurements at 293 K, 77.3 K and 4.2 K
Thermal cycling from 425 K to 77.3 K
Re-calibration and comparison with initial calibration
6
5
7
Short-term additional thermal cycling from 425 K to 77.3 K
8
Fig. 1. A schematic of the experiment.
of the TVO sensors can be caused by individual features of the TVO resistors and also with different conditions during calibration and measurements. Thus, the calibration is carried out with thermally conductive silicon grease between sensors and a copper comparison block in vacuum, and a temperature rate during cooling down to 4.2 K is rather low––about 0.001 K/s. Conversely, the test measurements are done with liquid nitrogen or liquid helium around the sensors at atmospheric pressure, and the temperature rate while cooling down to 4.2 K is rather fast––about 50 K/s. Then a series of experiments was carried out with thermal cycling of the selected sensors between 425 and 77.3 K (liquid nitrogen)––procedure 5. There were two possibilities to warm up the sensors in a furnace: vacuum environment and with hot air. The second way was chosen to provide harder conditions (presence of oxygen) with respect to a real case when warming up can be performed in vacuum. The temperature in the furnace with hot air was regulated with deviation of ±2 K around 423 K (150 C), so the maximum temperature was 425 K. The exposition time at this temperature was about 1 h for the first 50 cycles and 10 min for the rest 50 cycles. A comparison of the readings of the sensors with initial calibration curves––procedure 6––was performed at room temperature, in liquid nitrogen and liquid helium about 20 h after thermal cycling. From time to time, additional measurements at the same temperatures were also done in a day, in a week and in a month: it was done after the 10th, 15th, 20th and 25th cycles. We kept the sensors at room temperature between additional measurements. After 100th cycle, additional measurements were done in 1 week and then in every month. The measurements of TVO resistances were made by means of a new temperature monitor of our own production. This is a box of 180 · 76 · 24 mm3 connected to COM-port (RS232) of a personal computer. A four-lead technique is used to measure the resistance of the temperature sensor with respect to the precision reference resistor. To avoid the influence of parasitic voltages,
measurements are performed with a direct current source whose polarity can be changed. The main characteristics of the temperature monitor are as follows: the number of measured channels/sensors can be from 1 up to 15; the range of measuring current is from 0.5 lA to 5 mA; the range of measured resistances, R, is from 1 X to 100 kX; the accuracy of measurements is DR=R 6 0:01%; the time to measure all the channels is about 1.6 s; the sensors are connected in series. A mercury (Hg) thermometer of ±0.1 K accuracy was used to measure the reference value at room temperature. Our preliminary experiments have shown that differences between readings of RIRT-1 and the temperatures of saturation in liquid nitrogen (LN2 ) and liquid helium (LHe) were ±0.03 and ±0.002 K, correspondingly. Inasmuch as these values are significantly less than the possible instability of the TVOresistors, the temperatures of saturation Ts have been used as the reference values while measuring in LN2 and LHe. Corresponding depths of immersion of the sensors to dewars were the same during all the measurements. Since the initial deviations of the tested TVO-sensors are different, it would be useful to determine a zero point for all the sensors in order to present the results for comparison. To do this, the following procedure was used. The initial readings of all the tested sensors before warming up to 425 K (procedure 3) were measured at T 293 K (ambient air), Ts 77:3 K and Ts 4:2 K, and the values of dT0 ¼ TTVO Ts (or TTVO THg ) for each sensor were calculated, where TTVO and THg are temperatures of the TVO sensor and the mercury thermometer, respectively. After thermal cycling (procedure 6) the corresponding readings dT1 ¼ TTVO Ts were found, and the results were presented as DT ¼ dT1 dT0 versus N where N is a number of thermal cycles. The readings of the carbon–glass temperature sensor CRT-2 [4], calibrated 5 years ago, were used as additional reference while measuring in LN2 and LHe after the 10th cycle: DTCRT ¼ dTCRT dTs , where TCRT is calculated by means of its calibration polynomial. This reference sensor was not treated with thermal cycling. Its instability is estimated as DT =T 6 0:15%.
Y.P. Filippov, T.I. Smirnova / Cryogenics 44 (2004) 735–739 1 0.5 0
∆T , K
Finally, four chosen sensors were re-calibrated and a full-scale comparison with initial calibration curves was carried out––procedure 7. Afterwards, an additional thermal cycling––procedure 8––was done for the recalibrated sensors, and again the comparison with new calibration curves was carried out.
737
0
1
2
3
4
5
-0.5
6
7
8
9
1 0
1 1
1 2
1 3
1 4
1 5
1 6
1 7
1 8
1 9
2 0
2 1
2 2
2 3
2 4
2 5
2 6
2 7
2 8
2 9
293 K
-1 -1.5 -2
3. Results and discussions
CRT 449
2916 458
3215 459
354 4515
-2.5
1 2 3 4 5 6 7 8 9 10 13 15 16 18 20 21 23 25 N 1d 1w 1m 2w 1m 1d 1w 1m 1d 1w 1m
0.2
3.1. 100-time thermal cycling
0.1 0 -0.1
∆T , K
-0.2 -0.3 -0.4 -0.5
77.3 K
-0.6 -0.7
CRT 354 459
-0.8
2916 449 4515
3215 458
-0.9 5
0
CRT 354 459 0
1
2
3
4
5
6
7
8
9
10
1
1
12
1
3
1
4
1 5
1
6
1
7
1 8
1 9
2916 449 4515 20
2
1
2
2
23
3215 458 2
4
2
5
26
2
7
2 8
-5
∆T , mK
At the beginning, three sensors (#2916, #3215 and #354) were tested during 10 cycles. Then the second group of four sensors (#449, #458, #459 #4515) was tested separately also during 10 cycles. Immersions in liquid helium were not always made: the corresponding points are absent in the plot in this case. Afterwards these seven sensors were tested together up to 100 cycles. The results for the first 25 cycles, corresponding to procedure 6 in Fig. 1, are given in Fig. 2. Noteworthy is that temperature shifts of more than )2 K at 293 K, )0.5 K at 77.3 K and )20 mK at 4.2 K appear for sensor #354 right after the first thermal cycle. During 10 cycles, one can observe a tendency of DT to grow for rest of the sensors mainly within (0–0.5 K) at 293 K and to decrease within (0.1 to )0.3 K) at 77.3 K and (0 to )10 mK) at 4.2 K. A post-thermal cycling period (marked as 1d, 1w and 1m in Fig. 2) leads to reduction of DT at 293 K by 0.4 K approximately although the values of DT remain almost the same at 77.3 K, and one can see some DT -values decreasing at 4.2 K. The next noticeable result was observed for sensor #459 after the 16th cycle: DT became about )1.0 K at 293 K, )0.7 K at 77.3 K and )19 mK at 4.2 K. This sensor showed a maximum shift of )1.66 K at 293 K and )22 mK at 4.2 K a week after the 20th cycle. In its turn, the shifts for sensor #354 became closer to the DT values for rest of the five sensors after the 16th cycle. Except sensor #459, the shifts for six sensors decreased down to (0.1 to )0.7 K) at 293 K, ()0.1 to )0.35 K) at 77.3 K and ()5 to )11 mK) at 4.2 K after the 25th cycle. As for sensor #459, its DT values became about )1.4 K at 293 K, )0.8 K at 77.3 K and )23 mK at 4.2 K after the 25th cycle, i.e. 1 month after this cycle. As it was expected, the readings of CRT-2 remained approximately the same during all the experiment. One can note that the time to complete this part of the experiment required about 6 months. The results of further thermal cycling are shown in Fig. 3. One can see that the temperature shifts were relatively stable for all the sensors at all the temperatures after the 25th cycle including the 100th cycle and the three-month period after thermal cycling. The differences in the shifts for TVO sensors remained approximately the same, and insignificant deviations or
-10 -15 -20
4.2 K
-25
1 2 3 4 5 6 7 8 9 10 13 15 16 18 20 21 23 25 N 1d 1w 1m 2w 1m 1d 1w 1m 1d 1w 1m
Fig. 2. Temperature shifts DT versus the number of thermal cycling N and the additional period after thermal cycling––d (day), w (week), m (month): initial part.
oscillations of DT can be explained, in particular, by the errors of measurements and instability of the sensors. The time to complete thermal cycling from 30 to 100 and post-cycling measurements was about 6 months as well. So, the total experimental period was about 1 year. In addition, it is necessary to emphasize that no mechanical defects or cracks were revealed in the ceramic shell of the TVO resistors during all the experiment. In its turn, a common distinguishing feature appeared: the green color of all the sensor shells was becoming deeper tinged with brown due to oxidation at 425 K. However this does not matter for practical application. 3.2. Re-calibration Five months after completing the thermal cycling, four sensors––#2916, #354, #459 and #4515––were calibrated again, and the results of the comparison with the initial calibration curves are shown in Fig. 4. As it is seen, the best sensor #2916 has demonstrated a remarkable ability to reproduce the initial calibration
738
Y.P. Filippov, T.I. Smirnova / Cryogenics 44 (2004) 735–739 1 2916
3215
354
449
458
459
4515
0 .5
∆T , K
0 -0 .5
293 K
-1 -1 .5
25 1d 1w 1m
30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 N 1w 1m 2m 3m
0 -0.1
∆T , K
-0.2 -0.3 -0.4 -0.5 CRT
2916
3215
354
449
458
459
4515
-0.6 -0.7
77.3 K
-0.8 -0.9 0
to 70 K. As for the worst sensor #459, its maximum values of dT =T 1:3% were revealed near the temperature of 150 K, and dT =T were )0.6% at 3.0 and 4.2 K. Negative values of dT mean that the resistances of the sensors are increased due to some defects in the sensitive parts and perhaps in the contact parts caused by thermal cycling. One can note that a good agreement (dT =T < 0:1%) exists between the temperature shifts after procedure 6 of the whole procedure (Fig. 3) and re-calibration procedure 7 (Fig. 4) for sensors #459 and #4515 at 293, 77.3 and 4.2 K. As for sensors #2916 and #354, there is a good agreement for them at 293 K ()0.12 K against )0.16 K for #2916 and 0.48 K against 0.40 K for #354). However, deviations of about 0.15 K at 77.3 K and 6 mK at 4.2 K were found for these sensors. They can be explained as a result of different conditions during calibration and measurements and also with individual features of the TVO resistors commented above in item 2.
-5
∆T ,mK
3.3. Additional thermal cycling -1 0
4.2 K
-1 5 CRT
2916
3215
354
449
458
459
4515
-2 0
-2 5
25 1d 1w 1m
30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 N 1w 1m 2m 3m
Fig. 3. Temperature shifts DT versus the number of thermal cycling N and the additional period after thermal cycling––d (day), w (week), m (month): continuation.
0.2 0
It was interesting to estimate the behavior of the sensors after re-calibration: to make sure that the readings of the sensors remained stable and to demonstrate a final quality of the sensors. In principle, one can suppose that a qualitative picture could look like results around the 30th cycle. One can see that some growth of temperature shifts observed for the 30th cycle for 293, 77.3 and 4.2 K, and then the DT values may be approximately the same (Fig. 3). After re-calibration, an additional short-term thermal cycling between 425 and 77.3 K was carried out in two weeks. The results of measurements for the re-calibrated sensors are presented in Fig. 5 after the 1st (101st), 3d (103d) and 5th (105th) 0.4
-0.4 -0.6
∆T , K
δ T/ T, %
-0.2
2916
-0.8
35 4
-1
45 9 -1.2
0 -0.2
4515
101
-1.4
3
10
Temperature, K
100
300
Fig. 4. Comparison of the calibration curves: dT =T ¼ ðT1 T0 Þ=T , where subscripts 1 and 0 refer to new and initial calibrations.
105
1d
1w
∆T , mK
N 77.3 K
101
curve: its maximum deviation dT =T does not exceed )0.12% at 150 K that corresponds to dT ¼ 0:18 K. The temperature shifts of sensor #354 are not greater than )0.2% at 20 K although this sensor was showing the maximum temperature shifts DT during the first 10 cycles (Fig. 2). The typical sensor #4515 has shown shifts dT =T from )0.26% to )0.6% in a range from 4.2 to 70 K and from )0.036% to )0.6% in a range from 293
103
0.16 0.12 0.08 0.04 0 -0.04
∆T , K
1
293 K
0.2
103
105
1d
1w
N
5 3 1 -1
4.2 K
2916
354
459
4515
CRT
Fig. 5. Temperature shifts DT versus the number of thermal cycling N and the additional period after thermal cycling–– d (day), w (week).
Y.P. Filippov, T.I. Smirnova / Cryogenics 44 (2004) 735–739
additional cycles and after 1 day and 1 week. The results are presented as DT ¼ dT1 dT0 versus N (including CRT-2 sensor) that was commented above in item 2. As it is supposed, one can see a relatively small growth of DT for the 101th cycle at all the temperatures for all the sensors: up to 0.3 K at 293 K, 0.15 K at 77.3 K and 0.004 K at 4.2 K. For the 103th and 105th cycles, the temperature shifts remained the same in the limits of the accuracy of the measurements. One day and 1 week after thermal cycling, some expected decrease of DT by about 0.1 K at 293 K and 0.06 K at 77.3 K is observed. As for the temperature of 4.2 K, the temperature shifts for all the sensors are practically the same as during the thermal cycling. These results can be estimated as very good ones. In addition, one can note that the behavior of the former worst sensor #459 (see Fig. 4) looks approximately the same in Fig. 5 as for the best sensor #2916.
739
racy for the practical usage The structures of the sensitive parts/elements, and subsequently, the resistances of the sensors can change during the first twenty cycles. Afterwards the readings of the sensors remain stable: the corresponding deviations do not exceed the value of instability expected for the TVO-resistors. In order to use the TVO-sensors in the range from 4.2 to 425 K with relatively high accuracy––DT =T 6 0:25%, one needs to carry out 25 times thermal cycling between 425 and 77.3 K with subsequent calibration.
Acknowledgement Many thanks to our colleague V.M. Miklaeyv for his help to re-calibrate the temperature sensors.
References 4. Conclusions The influence of additional thermal cycling between 425 and 77.3 K on the readings of the TVO temperature sensors prepared in the usual way––preliminary thermal cycling from 373 to 77.3 K during 25 times, is as follows. There are two types of sensors: the majority (five of seven) for which the maximum temperature shifts DT =T are relatively small––down to )0.25% at 293 K, )0.5% at 77.3 K and )0.4% at 4.2 K, and the minority (two of seven) for which the values of DT =T can reach down to )0.7% at 293 K, )1.0% at 77.3 K and )0.6% at 4.2 K, approximately. These deviations can be considered as satisfactory accu-
[1] Suesser M. Characteristics of the TVO temperature sensors. In: Proceedings of the ICEC17, Bournemouth, UK, 1998, p. 699–702. [2] Suesser M, Wuechner F. Mechanical behavior of carbon ceramic TVO temperature sensors. Cryogenics 2001;41:213–5. [3] Balle C, Casas J, Rieubland JM, Suraci A, Togny F, Vauthier N. Influence of thermal cycling on cryogenic thermometers. In: Advance in cryogenic engineering, vol. 45B, Kluwer Academic/ Plenum Publisher, New York, Boston, Dordrecht, London, Moscow; 2000, p. 1817–23. [4] Dedikov YA, Filippov YP. Characteristics of Russian cryogenic temperature sensors. In: Proceedings of the ICEC18, Mumbai, India, 2000, p. 627–30. [5] Filippov YP, Kovrizhnykh AM, Miklayev VM, Sukhanova AK. Metrological systems for monitoring two-phase cryogenic flows. Cryogenics 2000;40:279–85.