CHARACTERISTICS OF RUSSIAN CRYOGENIC TEMPERATURESENSORS UNDER MAGNETIC FIELDS†‡†

Dedikov Yu.A. , Filippov Yu.P. and Kytin G.A.
†National Scientific and Research Institute for Physical Technical and Radio-technicalMeasurements - VNIIFTRI, Mendeleyevo 141570, Moscow Region, Russia‡Joint Institute for Nuclear Research, Dubna 141980, Moscow Region, Russia

Abstract
The report presents the results of our activity during
many years in the field of cryogenic thermometry andmetrology applied to superconducting devices operating inthe magnetic fields e.g. subsystems of accelerators anddetectors. The equations to calculate the temperature shifts
due to the magnetic fields for temperature sensors aregiven.

1 INTRODUCTION
Physical installations with superconducting magnets
require efficient systems for monitoring the operation
characteristics of the cooled devices and cryogens. The
value of temperature is one of the main parameters todetermine the state of the cryogen or cooled device. This
report presents the information about four types of
Russian commercially available cryogenic resistive
temperature
sensors
investigatedatcryogenic
temperatures and under magnetic fields up to 9 T. Theyare platinum, rhodium-iron, carbon-glass and carbon
TVO-resistors.

2 CHARACTERISTICS OF THE
SENSORSThe detailed characteristics of all the thermometers arepresented in [1,2]. Briefly they are as follows.
Rhodium-iron (RIRT) and platinum (PRT) resistive
temperature sensors. The measured range is from 0.5 K to373 K and from 13.8 K to 373 K for RIRT-1 and PRT-5
modifications; resistance at 273.15 K is 100 Ohm, self
heating - 2 mK, diameter - 3.7 mm, length - 40 mm, mass- 2 g, accuracy - ± 1 mK for both sensors; stability is 0.5
mK and 0.3 mK per year for RIRT-1 and PRT-5,correspondingly. The sensors RIRT-1 and PRT-5 areincorporated in the Russian national standard of theInternational Temperature Scale of 1990 (ITS-90). Othermodifications of these thermometers - RIRT-2, RIRT-3,RIRT-4 and PRT-5V, PRT-4, PRT-4M are also produced.
They are intended for calibration with the reduced
accuracy, precision laboratory measurements andoperation in radiation environment; their length can be of
20...40 mm at the same diameter. For example, theaccuracy of RIRT-2 and PRT-5V is 5 and 10 mK,correspondingly.
Carbon-glass resistive temperature sensor: model CRT-2.
Its characteristics are as follows: the measured range isfrom 2 K to 300 K; diameter - 2.2 mm, length - 14 mm,
mass - 1 g, self-heating - ≤ 3 mK; accuracy - 10 mK at(0.35 - 4) K, 30 mK@(4 - 27) K, 100 mK@(27 - 80) K
and 1.5 K@300 K; stability - 3 mK/year at (0.35 - 4) K
and 10 mK/year@(27 - 80) K. This sensor is intended forlaboratory measurements, particularly, at the highmagnetic field and irradiation.
Carbon resistive temperarure sensor based on the TVO
resistor. This type of the thermometer is well known[1,2,3,4,5]: for example, several hundreds TVO are usedsuccessfully in superconducting accelerator of nuclei Nuclotron at JINR, Dubna [4]. Physical configuration is arectangular prism of 8 mm length and 1.3×2.4 mm2 crosssection with two copper leads. It has ceramic and glasscoats to provide a hermetic seal, and can be used in theenvironment combining moisture, corrosion, vibration,high and low temperatures. One of the features of theTVO-sensors is zero inductance and high electric
insulation resistance - up to 5000 MOhm. The nominalvalues can be of 910, 1000 or 1100 Ohms. The uncertainty
caused by instability of the resistance is estimated as ∆T/T
≤ ±0.25 % for the first class and ±0.5 % for the second
one. It is admitted to warm the sensor to 373...400 K
without changing its calibration. This sensor can berecommended for routine measurements in the highmagnetic field and radiation environment.

3 TEMPERATURE SHIFTS DUE TO THE
MAGNETIC FIELD
The investigated sensors can be divided into twogroups: TVO and CRT with negative temperature
coefficient and low temperature shift due to the magneticfield, ∆T = T(B) - T(0), and RIRT and PRT with positive
temperature coefficient and comparatively high ∆T at low
temperatures. Let us consider these groups.
CRT and TVO sensors. An important advantage of bothcarbon thermometers is that their readings practically do
not depend on the orientation in the magnetic field. The
values of ∆T/T(0) for CRT with lowest and highest
sensitivity are shown in Figure 1. The analysis has shown

that the values of the magneto-resistance, ∆R = R(B)-R(0),for CRT sensors are described very accurately by theequation

0,00
4.2K, 2T-0,05-0,102K, 2T
2K, 4T-0,15∆R = A×Bn ,(1)-0,20
4.2K, 4T

where lnA = Σ ai(lnT) , n = Σbi(lnT) , i = 0 - m, and m =2
for the range from 2 K to 5 K and m = 4 for the range
from 2 K to 80 K. The corresponding deviations of theexperimental points from curve (1) do not exceed ±3 mKfor the batch of 8 investigated sensors. To determine theparameters in Equation (1), it is necessary to have theinitial calibration curve at B = 0 and to measure themagneto-resistance, for example, in 5 points for the range(2-5) K and 10 points for (20-80) K. Usually, there are noproblems to calculate the value of the magnetic field, B,
and estimate its direction in the point of the sensor
mounting within a real system. This allows one tocalculate the corresponding temperature shift due to themagnetic field ∆T = ∆R(dT/dR).
i∆T, K-0,25
i-0,30-0,352K, 8T-0,40-0,45

4.2K, 8T-0,50-0,55
0,81,0

1,2

1,4

1,6

1,82,02,22,42,62,83,0|1/S| = (R/T)(dT/dR)

Figure 2: Temperature shift, ∆T, due to the magnetic field,
B, versus sensitivity, 1/S, for different CRT-2.
five TVO sensors are presented. One can see that all theexperimental data can be fitted by a very simple equation:∆T = (C2B - C3)/S(3),which is valid as the first approximation for the ranges(1.8 - 4.2) K and (0 - 9) T: the maximum deviation of themajority of the experimental points does not exceed 0.02
K. The coefficients are as follows: C2 = 0.0089, C3 = 0 at
(0 - 2.25) T, C2 = 0.023, C3 = 0.032 at (2.25 - 4.5) T and C2= 0.0263, C3 = 0.047 at (4.5 - 9) T. The calculations
according to this equation are in good agreement with theresults based on the data [6] for eight TVO sensors tested
in the range from 1.8 K to 4.2 K: the differences at S = 1are 0.002 K at 3 T, 0.005 K@ 6 T and 0.015 K@ 9 T.
0,00

Figure 1: Relative temperature shift, ∆T/T(0), due to themagnetic field, B, versus temperature, T, for CRT-2.

-0,05
B=2T-0,10∆T = A0(B,T) + A1(B,T)/S-0,15∆T, K

Noteworthy that the behavior of the arbitrary chosen CRT2 sensors in the magnetic field at helium temperatures canbe described by the equation

B=4T-0,20-0,25
B=6T(2),-0,30

N91
N92
N93
N96
N100-0,35

where S = (T/R)(dR/dT) is dimensionless sensitivity. Eq.
(2) is valid for the ranges (2-6) K and (0-8) T. The
maximum deviation of the experimental points does notexceed 0.02 K, see Figure 2. To calculate ∆T by means ofEquations (2), it is necessary to have the calibration curveat B = 0 and to use an iteration algorithm to find thethought value at the estimated B.
The values of relative magneto-resistance ∆R/R(0) and∆T/T(0) for the batch of 8 TVO sensors can be found in[6]. For example, ∆R/R(0) can be described by theequation ∆R/R(0) = e(C0−C1T). Noteworthy that dependenceof ∆T on B and T for these sensors looks similar on thoseshown in Figure 2 for CRT-2. It is illustrated with Figure
3 where new experimental data for-0,40
1,2

1,4

T=2.8, 3.0, 3.4, 3.8, 4.25 K

1,6

1,82,0B=8T

2,22,4|1/S|=R/T(dT/dR)

Figure 3: Temperature shift, ∆T, due to the magnetic field,
B, versus sensitivity, 1/S, for different TVO sensors
To obtain a more accurate calculation, it is necessary tocarry out a calibration of a TVO sensor in the magneticfield. Thus, if the equation∆R/R(0) = ΣAik(lnT)i B[th(CiT)+1]
is used, one can calculate ∆T(B, T) with δT<± 0.01 K.

(4)

RIRT and PRT sensors. Temperature shifts, ∆T, due to theperpendicular magnetic field and ∆T/T(0) for RIRT areillustrated by Figures 4 and 5. One can see that thesevalues are significantly larger than for CRT-2 and TVO.
However, the way to determine ∆T for RIRT with theaccuracy of 0.01 K can be derived. Processing theexperimental data for this sensor has shown that if thecalibration curve for RIRT is known for the case B=0, thevalues ∆T(B, T) can be calculated with the accuracy of
0.01 K for the ranges (3 - 80) K and (0 - 7) T by Equation(5)ln∆R(B, T) = lnA + n(lnB) + p(lnB)2(5),

where A, n and p depend only on the temperature.
Influence of the orientation of the RIRT thermometers in
the magnetic field can be taken into account by the Qfactor which is the ratio between the values of ∆T at
perpendicular and parallel orientation of the magnetic fieldQ = ∆T⊥/∆T|| = 1.053 + 0.103lnT(6).

This is valid for the temperatures from 3 K to 20.4 K withthe deviation of about ±0.5 %.

5

2.4T
3.62T
4.8T
6.0T
6.5T

B=

∆ T, K

4

32

10020

40

60

8T,KFigure 4: Temperature shift, ∆T, due to the perpendicularmagnetic field, B, versus temperature, T, for RIRT.
8070

2.4T60B=∆T/T(0), %50

3.62T
4.8T
6T
6.5T

40302010002040608T,K

Figure 5: Relative temperature shift, ∆T/T(0), due to theperpendicular magnetic field, B, versus temperature, T, for
RIRT.

As for the platinum thermometers, their behavior in themagnetic field can be described by the relation [7]∆WM(B, W) = Σ Ai(lnW)i⋅Bn(W), i=0...12(7),where W = R(T)/R(273.15 K) is the standard relative
resistance of the sensor at B=0. The deviations of the∆WM-values from the experimental points do not exceed
0.02 K for the ranges (30 - 190) K and (0 - 7) T. Influenceof the orientation of the PRT sensors in the magnetic field
and a procedure to calculate the temperature shifts due tothe magnetic field can be found in [7]. The typical valuesof ∆T/T for them in the perpendicular magnetic field areapproximately as follows: 26 % at 20.2 K and 6.5 T,
2.3 % @ 40.3 K and 6.5 T, 0.28 % @ 80 K and 6.5 T [7].

5 CONCLUSIONS
Russian cryogenic thermometers are able to provide
reliable measurements of temperatures in physical andindustrial installations under conditions combining
magnetic fields and cryogenic temperatures of a wide
range: their choice depends on the technical requirements.
To calculate the temperature shifts due to the magnetic
fields for the carbon sensors with the accuracy about 0.02
K, one can use relations (2), (3) and the initial calibration
curves T(R,B=0). More accurate calculations for theconsidered sensors are possible by means of equations (1),(4)÷(7): in this case one needs to obtain several
experimental points to determine the corresponding
coefficients.
REFERENCES[1] Yu.A.Dedikov and Yu.P.Filippov, Characteristics ofRussian Cryogenic Temperature Sensors, in: Proc. ofthe ICEC18, Mumbai, India, 2000, p.627-630.
[2] M.S er, Characteristics of the TVO TemperatureSensors, in: Proc. of the ICEC 17, Bournemouth, UK,1998, p. 699-702.
[3] V.I.Datskov and J.G.Weisand II, Characteristics ofRussian Carbon Resistance (TVO) Cryogenic
Thermometers, Cryogenics, 34, 1994, p.425-428.
[4] A.M.Baldin et al., Cryogenic System of the Nuclotron- a New Superconducting Synchrotron, in: Advancesin Cryogenic Engineering, vol.39a, Plenumm Press,
New York, 1993, p. 501-508.
[5] Ch.Balle, J.Casas, J.M.Rieubland, A.Suraci, F.Tognyand N.Vauther, Influence of Thermal Cycling on
Cryogenic Thermometers, in: Advance in Cryogenic
Engineering, 45, 2000, Plenum Press, New York (tobe published).
[6] Yu.P.Filippov and A.K.Sukhanova, Behaviour of theTVO Temperature Sensors in the Magnetic Fields andunder Gamma Irradiation, in: Proc. of the EPAC2000,Vienna, Austria, p.2278-2280.
[7] G.S.Abilov and I.A.Razhba, Characteristics of theLow Temperature Resistive Thermometers in
Magnetic Fields and the Ways of Approximation, in:"Metrologic Support of Thermal Explorations at Low
Temperatures", Moscow, VNIIFTRI, 1988, p.59-73(in Russian).