J.15.7 Calibration tests for PTC thermistors
J.15.7.1 Ceramic thermistors are not influenced by the sequence in which the calibration tests of J.15.7.4 to J.15.7.8 are conducted on the samples. However, polymeric types may be influenced due to the nature of the material. Hence, for polymeric types of thermistors, it is recommended to perform the test of J.15.7.4 at the end of all the calibration tests.
J.15.7.2 In the "as-received" condition, each PTC thermistor sample shall be subjected to the tests specified in Table J.6 and shall comply with the criteria for each test as specified in Table J.6.
J.15.7.3 Following the tests described in J.17.17 a), the same PTC thermistor samples shall be subjected to the tests specified in Table J.6 and shall comply with the criteria for each test as specified in Table J.6. For PTC sensors, the test results shall comply with the criteria for each test as specified in Table J.7.
Table J.6 – Sequence of calibration and conditioning tests for PTC thermistors
Type of PTC thermistor
Calibration tests performed on samples
before the conditioning tests specified in J.17.18 a
Compliance criteria designation (before
conditioning) b
Calibration tests performed on thermistor
samples after conditioning tests specified in J.17.18 a
Compliance criteria designation
(after conditioning) b Self-controlled
heater R/T A Ts D
Ts In
In
Motor starter R/T A Ts D
Ts In
In
Degausser R/T A Ts D
Ts In
In
Current limiter R/T B TT E
Ts TT Iss
Ih
Sensor R/T C R/T F
R/T - R/T measurement for PTC thermistors – all types (J.15.7.4) Ih - Hold current test for PTC current limiters (J.15.7.5)
TT - Time-to-trip test for PTC current limiters (J.15.7.6) Ts - Surface temperature test (J.15.7.7)
In - Inrush current (compliance is determined by measurement, J.15.7.8) Iss - Steady-state current (compliance is determined by measurement)
A - Resistance at 25 °C, surface temperature and inrush-current values shall be within the declared deviation tolerance specified by the manufacturer.
B - Resistance at 25 °C, surface temperature, steady-state current and time-to-trip values shall be within the declared deviation tolerance specified by the manufacturer. The thermistor shall maintain the hold current for the time at the ambient temperature specified by the manufacturer, without tripping.
C - The temperatures corresponding to the switching resistance (Rsw) and two additional points, located above and below Rsw on the R/T curve shall be within the declared deviation tolerance specified by the manufacturer.
D - The surface temperature and inrush-current values shall be within the declared drift tolerance specified by the manufacturer.
E - Time-to-trip values shall be within the declared drift tolerance specified by the manufacturer.
F - The temperatures corresponding to the switching resistance (Rsw) and two additional points, located above and below Rsw on the R/T curve shall not vary from the corresponding as-received values by more than indicated in Table J.7.
a Test abbreviations
b Compliance criteria
Table J.7 – Classes for PTC sensing thermistors
Property
Class No.
C1 C2 C3 C4
Temperature drift, K for a given resistance ±0,5 ±1,0 ±2,0 ±5,0
Temperature values should be “normalized” to the Kelvin scale when determining the temperature drift.
J.15.7.4 R/T measurement for PTC thermistors
J.15.7.4.1 Thermistor samples shall be placed in a full draft circulating-air oven or fluid medium, such as silicon oil with the temperature maintained within ±1 K of the temperature specified for the test. The test shall be conducted at various temperatures starting at room ambient temperature through the switching temperature (Tsw) and not exceeding the thermal runaway temperature (TR) of the R/T curve. The resistance is be measured by an ohmmeter at as many temperatures as required to create a complete R/T curve.
J.15.7.5 Hold current (Ih) test for PTC current limiters
J.15.7.5.1 A current limiting thermistor shall maintain the specified hold current (Ih) for the time specified by the manufacturer at the ambient temperature specified by the manufacturer without tripping.
J.15.7.6 Time-to-trip test for PTC current limiters
J.15.7.6.1 A current limiting thermistor with a time-to-trip specification shall trip at the specified trip current (It) and corresponding rated voltage (Vr) within the specified time-to- trip. A thermistor with multiple trip currents and times shall be tested at the maximum and minimum specified currents. The current is not to exceed the maximum current (Imax) point on the time-to-trip versus current curve.
J.15.7.6.1.1 A current limiting thermistor, as declared in item 82 of Table J.5, shall trip at the declared trip current (It) and corresponding rated voltage (Vr) within the specified time- to-trip.
J.15.7.7 Surface temperature test
J.15.7.7.1 The surface temperature (Ts) of a PTC thermistor shall be measured using thermocouples or equivalent devices. For a PTC thermistor other than a current limiter, the surface temperature (Ts) shall be measured while the thermistor is operating at maximum voltage (Vmax) and steady-state current. For a PTC current limiter, the surface temperature (Ts) shall be measured under two conditions:
a) operating condition in hold state where the device shall be operated at its rated maximum voltage (Vmax) and rated hold current (Ih), and
b) operating condition in tripped state where the device shall be operated at rated maximum voltage (Vmax) and rated steady-state current (Iss).
See Table J.2.
J.15.7.8 Inrush current measurement
J.15.7.8.1 For PTC thermistors intended to be used as self-controlled heaters, motor starters or degaussers, the inrush current shall be measured using an oscilloscope while the thermistor is operating at maximum voltage under rated load.
J.15.8 Calibration tests for NTC thermistors
J.15.8.1 In the "as-received" condition, each NTC thermistor sample shall be subjected to the tests specified in Table J.8 and shall comply with the criteria for each test as specified in Table J.8.
J.15.8.2 Following the tests described in J.17.17 b), the same NTC thermistor samples shall be subjected to the tests specified in Table J.8 and shall comply with the criteria for each test as specified in Table J.8. For NTC sensors, the test results shall comply with the criteria for as specified in Table J.9.
Table J.8 – Sequence of calibration and conditioning tests for NTC thermistors
Type of NTC thermistor
Calibration tests performed on samples before the conditioning
tests specified in J.17.18 a
Compliance criteria designation (before
conditioning) b
Calibration tests performed on thermistor
samples after conditioning tests specified in J.17.18 a
Compliance criteria designation (after
conditioning) b Inrush-
current limiter
R/T A Ts C
Ts In
In
Sensor R/T B R/T D
Beta
R/T - R/T measurement for NTC thermistors (J.15.8.3) Ts - Surface temperature test (J.15.8.4)
Beta - Resistance (R25) and beta value (B) test for NTC thermistors (J.15.8.6) In - Inrush current (compliance is determined by measurement (J.15.8.5)
A - Resistance at 25 °C, surface temperature, and inrush-current values shall be within the declared deviation tolerance specified by the manufacturer.
B - The resistance at two or more temperature points on the R/T curve and the beta value (if declared) shall be within the declared deviation tolerance specified by the manufacturer. One of the temperatures shall be at 25 °C.
C - The surface temperature and inrush-current values shall be within the declared drift tolerance specified by the manufacturer.
D - The resistance at two or more temperature points on the R/T curve shall not vary from the respective "as received" temperatures on the "as-received" R/T curve by more than indicted in Table J.9. One of the temperatures shall be 25 °C.
a Test abbreviations
b Compliance criteria
Table J.9 – Classes for NTC sensing thermistors
Property
Class No.
C1 C2 C3 C4
Temperature drift for a given resistance ±0,5 ±1,0 ±2,0 ±5,0
Temperature values should be “normalized” to the Kelvin scale when determining the temperature drift.
J.15.8.3 R/T measurement for NTC thermistors
J.15.8.3.1 Thermistor samples shall be placed in a full draft circulating-air oven or fluid medium, such as silicon oil with the temperature maintained within ±1 K of the temperature specified for the test. The test shall be conducted at various temperatures, starting at room ambient temperature and not exceeding the maximum declared sensing temperature (sensors) or the maximum surface temperature (Ts) determined in accordance with J.15.8.4
(inrush-current limiters). The resistance shall be measured at as many temperatures as required to create a complete R/T curve.
J.15.8.4 Surface temperature test (inrush-current limiting only)
J.15.8.4.1 The surface temperature (Ts) of a NTC inrush-current limiter shall be measured using thermocouples or equivalent devices while the NTC thermistor is being operating at maximum voltage (Vmax) and maximum current (Imax) with the rated capacitance value in parallel with the load. The temperature shall be within the manufacturer's specified limits. See Table J.8.
J.15.8.5 Inrush current measurement (inrush-current limiting only)
J.15.8.5.1 For an NTC inrush-current limiter, the inrush current shall be measured using an oscilloscope while the thermistor is operating at maximum voltage (Vmax) and maximum current (Imax) with the rated capacitance value in parallel with the load.
J.15.8.6 Resistance (R25) and beta value (B) test for NTC thermistors
J.15.8.6.1 The beta value (B) of a thermistor with a beta value (B) rating shall be within the limits specified by the manufacturer. The resistance (R25) of a NTC thermistor shall be measured at 25 °C followed by measurement of resistances R1 and R2 at temperatures T1 and T2 as specified by the manufacturer. The beta value (B) shall be calculated using the following formula:
B= (In R1 – In R2) / (1/T1 – 1/T2) where
B is the calculated beta value, R1 is the resistance at T1, R2 is the resistance at T2,
T1 is a temperature in K on the R/T curve specified by the manufacturer, and T2 is a second temperature in K on the R/T curve specified by the manufacturer.