QUALITY AND CERTIFICATION
MTP 1200-4 FURNACE — A NEW GRADE
OF THERMOCOUPLE VERIFICATION
Yu. O. Malyshev
Translated from Novye Ogneupory, No. 7, pp. 50 – 51, July 2009.
Original article submitted April 13, 2009.
Horizontal low-inertia tube furnaces MTP-2MR and MTP 1200-2 are considered in accordance with GOST
8.338–2002. Comparative characteristics are provided.
Keywords: horizontal tube furnace, thermocouple, metrological characteristics, GOST 8.338–2002, tempera
In this article we are talking about a well-known class of
metrological equipment, i.e. horizontal; tube furnaces. The
main specifications for furnace properties are given in GOST
8.338–2002 “Thermoelectric transducers. Verification proce-
– the working space should have a length from 500 to
600 mm and a diameter from 40 to 90 mm;
– the maximum operating temperature should not be be-
– the temperature gradient over the furnace axis (in its
central part) at 1000°C should not exceed 0.8°C/cm in a sec
tion with a length not less than 50 cm;
– the instability of temperature maintenance should not
be greater than 0.4°C/min.
In addition, GOST 8.338–2002 recommends use in a
horizontal furnace in some cases of a thin-walled nickel ves
sel 80 to 100 mm long. The vessel wall thickness and bottom
is not less than 5 mm. It is permissible to use a nickel unit of
appropriate dimensions with nests of the required diameter
and depth from 70m to 90 mm. A nickel vessel (or unit)
should be connected to the earthing circuit.
The furnace MTP-2MR is well known to many special
ists of the metrological services and metrology centers, that
over many years has been series produced by OAO NPP
Étalon. The furnace corresponds to all standard specifica
tions, but in spite of constant improvement the construction
has a number of drawbacks.
It is well known that above 700°C the mullite-corundum
ceramic, used in MTP-2MR heating furnaces, becomes elec
trically conducting. With this there is the probability of
flash-over of the heater in the body if an earthed levelling
unit or vessel is placed within the furnace working space.
Therefore, during operation it is not possible to earth the lev-
elling unit or vessel in the MTP-2MR furnace, and this elimi-
nates additional screening of the measuring circuit of the ver-
ification unit. In addition, the possibility of electrical
flash-over gives rise to a requirement for total switching of
the furnace from the electricity circuit during loading of the
next batch of thermometers for checking, and this leads to
disruption of the furnace heating regime.
Another disadvantage of the MTP-2MR furnace is the
marked difference in readings between a standard thermome
ter, placed in the working space of the furnace, and the con
trol unit indicator. In individual cases this difference reaches
30°C. In spite of the fact that the MTP furnace is not a tem
perature calibrator, the difference observed in its readings is
not standardized, and this gives rise to some inconvenience
for furnace operation, compelling the operator to remember
this difference and to consider it during operation.
It should be noted that the temperature gradient in the
MTP-2MR furnace is provided by means of a special wind
ing and special treatment for the heater insulation, but with
time the heat insulation properties change due to gradual
warm-up, and the heater wire after repeated heating - cooling
cycles gradually loses thermal contact with the heating tube.
With time these two processes lead to change in temperature
distribution within the furnace working space. It is almost
impossible to take these two processes into consideration.
This leads to a requirement for changing the heater insula
tion, and this is only possible with complete dismantling of
Refractories and Industrial Ceramics Vol. 50, No. 4, 2009
1083-4877/09/5004-0304 © 2009 Springer Science+Business Media, Inc.
OAO NPP Étalon, Omsk, Russia.