Rod thermostats with microswitches operate according to the rod-length expansion principle.
During this process, the change of the sensing-probe length (which depends on the temperature) is transmitted via an internal rod (that has a smaller expansion coefficient and that is fitted
in the thermowell) to a transmission unit equipped with a microswitch in the switching head.
The thermostats of the STMA series are used, for example, in the heating and air conditioning
industries.
Rod thermostats distinguish themselves by their high excess-temperature protection that functions independently of the control range (maximum. +345 °C), high response sensitivity (time
constant 8 s), and negligible low-ambient temperature influence at the switching head.
When the sensing probe is damaged or bent, the thermostat changes to "Safe status“ (heater
off).
Switching function
Temperature controller TR and temperature monitor TW
If the temperature on the temperature probe exceeds the setpoint value, the microswitch is activated by the transmission mechanics and the electrical circuit is opened or closed. If the temperature falls below the selected setpoint (by the amount of the switching differential), the
microswitch is reset to its initial position.
Temperature limiter TB
If the temperature on the temperature probe exceeds the set limit value, the electrical circuit is
opened and the microswitch is mechanically locked. The microswitch can be manually unlocked once the temperature has dropped by approx. 10 % of the scale range.
Temperature limiter TB with extra code 574
The additional N/O contact can be used as a signal contact.
Control ranges °CSwitching differential in °C Immersion tube length SActive immersion tube
length
Control ranges,
switching differential,
and immersion tube
length
-10 to +100
+5 to +160
0 to +300
0 to +75
4 ± 1100 mm100 mm
3 ± 0.7150 mm150 mm
+15 to +120
+5 to +160
0 to +240
0 to +80
2.5 ± 0.4200 mm200 mm
0 to +120
+20 to +200
+50 to +300
-80 to +100
0 to +50
1.9 ± 0.4250 mm250 mm
+20 to +150
0 to +200
-15 to +50
0 to +40
1.6 ± 0.4300 mm300 mm
0 to +80
Electrical dataSTMA-1STMA-2STMA-7STMA-7 / 574
Switching elementMicroswitch with
changeover contact
Microswitch with
changeover contact
Microswitch with N/C
contact and restart lock
Microswitch with N/C contact, restart lock, and additional signal contact
Maximum switching
capacity
230 VAC +10 %, 10 (2) A, cos = 1 (0.6)
DC 230 V +10 %, 0.25A
Operating data
Switching point accuracy
± 1.5% of the scale range, in the scale range center, referring to the switchoff point
in %
Allowable storage
-50 to +50 °C
temperature
Allowable ambient
-40 to +80 °C
temperature when in use
Rated positionAccording to DIN 16 257, rated position 0 to rated position 90 (different rated positions upon request)
Case
CaseAluminum diecast, surface with impact-resistant textured paint; lid: RAL 7032, bottom section: RAL 7015
Cable inletStandard: Clamping gland M 20 x 1.5
Available at extra cost: Cable screw-connection M 20 x 1.5 according to EN 50262 CuZn
Setpoint value settingSTMA-1STMA-2 / STMA-7
Switching point adjustable from the outside using the
rotary knob
Switching point adjustable with a screwdriver once the
case lid has been removed
Protection typeEN 60 529-IP 54
WeightApprox. 0.65 kg
Process connectionVersionMate rial
Plain cylindrical probeCollar Ø 19 mm between case and sensing probe
CuZn
(extra codes 574, 715, 764 can be retrofitted)
Screw-in sleeveThermowell as a screw-in sleeve, screw-in spigot shape A according to
DIN 3852/2 with fixing screw, immersion tube Ø 12 mm
Up to 150 °C CuZn, nickel plated /
As of150 °C CrNi
Extra code 715Loose screw-connection M 18 x 1 with counter nutCuZn nickel plated
Extra code 764Mounting flangeSheet steel, galvanized
Fixed screw-connectionWith hexagon, width across flats 27, thread G1/2CuZn nickel plated
ProbeDiameter 9 mmCuZn nickel plated
Insertion length S100, 150, 200, 250, and 300 mm
01STMA-1 temperature controllerTR with changeover contact
02STMA-2 temperature monitorTW with changeover contact
07STMA-7 temperature limiterTB with N/C contact
( 3 )Control / limit value range
Range in °CImmersion tube length in mm
0200 to +40300
0210 to +50250
015-15 to +50250
0230 to +75150
0240 to +80200 or 300
010-80 to +100200
017-10 to +100100
0260 to +120200
037+15 to +120150
043+20 to +150250
035+5 to +160100 or 150
0280 to +200250
044+20 to +200200
0290 to +240150
0300 to +300100
064+50 to +300200
( 4 )Process connection
10Plain cylindrical probe
20Screw-in thermowell
54Fixed screw-connection with hexagon (special model)
( 5 )Thread of process connection
00Without thread
13External thread G 1/2
( 6 )Material of process connection
46CuZn (brass)Only with process connection 10, 20, 54
20CrNi (stainless steel)Only with process connection 20
( 7 )Insertion length "S“
(immersion tube length)
100100 mm
150150 mm
200200 mm
250250 mm
300300 mm
( 8 )Extra codes
574Microswitch with N/C contact, restart lock,
and additional signal contact (only for temperature limiter)
715Loose screw-connection M 18 x 1 with locknut
764Mounting element
Data Sheet 601530Page 6/6
Ø 9 mm
Ø 12 mm
Note the dependency of the control range to the immersion
tube length!