1. Scope and Field of Application
This standard defines the terminology, product classification, technical specifications, testing methods, inspection rules, labeling, packaging, and other requirements for industrial bimetal thermometers (hereinafter referred to as thermometers).
The standard applies to temperature sensing components that consist of bimetallic elements and protective sheaths, featuring a circular dial with a measurement range from -80°C to +500°C.
2. References
ZBY 002: Basic environmental conditions and test methods for instrumentation, transportation, and storage.
ZBY 003: Packaging technical conditions for instrumentation.
ZBY 120: Working conditions for industrial automation instruments—temperature, humidity, and atmospheric pressure.
ZBY 122: Basic types, dimensions, and general technical requirements for pointer parts of industrial automation instruments.
ZBY 123: General rules for industrial automation instrumentation.
ZBY 247: Terminology for industrial automation instruments.
3. Terms and Definitions
In addition to ZBY 247, the following terms and definitions apply to this standard.
3.1 Axial type: The detection element axis is perpendicular to the dial plane.
3.2 Radial type: The detection element is parallel to the dial plane.
3.3 Insertion length: The distance from the lower end of the detection element to the mounting joint or the lower end of the tapered thread (see L in Figures A1–A4 in Appendix A).
3.4 Measuring length: The length of the detection element immersed in the measured medium.
4. Product Classification and Basic Parameters
4.1 Thermometers are classified into four types based on the installation method of the indicating device and detection component:
a. Radial type
b. Axial type
c. Universal type
d. Angular type
Mechanical and Electronic Industry Department, approved on June 12, 1988, effective January 1, 1989.
4.2 Dial nominal diameter: 60 mm, 100 mm, 150 mm.
4.3 Measurement range: Must comply with Table 1.
Table 1:
-80 to +40°C
-40 to +80°C
0 to 50°C
0 to 100°C
0 to 150°C
0 to 200°C
0 to 300°C
0 to 400°C
0 to 500°C
4.4 Accuracy grade: Thermometers have accuracy levels of 1, 1.5, (2.5).
Note: The accuracy level in parentheses is not recommended.
4.5 Detection element diameter and mounting thread: Must comply with Table 2.
Dial nominal diameter | Detection element diameter | Mounting thread
60 mm | 4 mm | M 16 × 1.5
100 mm | 8 mm | M 27 × 2
4.6 Insertion length: Available in 75, 100, 150, 200, 250, 300, 400, 500 mm.
Note: If longer than 500 mm, agreement between manufacturer and user is required.
4.7 Jacketed pressure rating: Should be selected from 1.0, 1.6, 2.5, 4.0, 6.4 MPa.
4.8 Installation connection types: Four types available (see Appendix A):
a. Adjustable pipe joint
b. Pipe joint (external thread)
c. Pipe joint (internal thread)
d. Fixed thread
4.9 Indication adjustment mechanism: Three types available:
a. No adjustment mechanism
b. External adjustment mechanism
c. Internal adjustment mechanism
5. Technical Requirements
5.1 Normal working conditions: Must comply with Table 3.
Table 3:
Ambient temperature (°C) | Relative humidity (%)
Covered area: -25 ~ +55 | 5 ~ 100
Outdoor area: -40 ~ +85 | 5 ~ 100
Note: Special conditions must be agreed upon between manufacturer and user.
5.2 Appearance, structure, and assembly quality:
a. No rust on parts; protective layer should be firm, uniform, and smooth.
b. Glass or transparent material on the surface must be clear and free of defects affecting reading.
c. Type, basic parameters, and dimensions must comply with Chapter 4.
d. Pointer and dial must follow ZBY 122 and ZBY 123. Pointer length (from pivot center to tip) must meet Table 4.
e. Distance between pointer and dial plane must be ≤ 5 mm.
f. Circular scale should be 270°–300°.
g. Pointer, dial, scale, and markings must not discolor or fade.
Table 4:
Dial nominal diameter | Pointer length
60 mm ≥ 23 mm
100 mm ≥ 36 mm
150 mm ≥ 57 mm
5.3 Basic error limits: Must comply with Table 5.
Table 5:
Accuracy level | Basic error (%)
1.0 of range ±1.0
1.5 of range ±1.5
(2.5) of range ±2.5
5.4 Hysteresis: Must not exceed the absolute value of the basic error limit.
5.5 Repeatability: Must not exceed half of the basic error limit.
5.6 Thermal stability: After maintaining the upper limit for the time specified in Table 6, the detection element must comply with 5.3.
Table 6:
Measurement upper limit (°C) | Holding time (h)
≤ 300 | 24
400 | 12
500 | 4
5.7 Time constant: Must be ≤ 40 seconds.
5.8 Vibration resistance: Must withstand 25 Hz frequency, 0.6 mm displacement amplitude, 24 hours of vibration. After test, thermometer must still meet 5.3 and no mechanical damage.
5.9 Position influence: Tilting 90° forward, backward, left, or right must not cause an indication change exceeding the basic error limit.
5.10 Pressure-resistant jacket: Must withstand 1.5× nominal pressure without damage or leakage.
5.11 Transportation and storage: Must pass tests for high/low temperature, impact, and drop according to ZBY 002. After test, must comply with 5.2, 5.3, 5.4, and 5.5.
6. Test Methods
6.1 Visual and tool inspection for appearance, structure, and assembly quality.
6.2 Basic error limit test:
6.2.1 Conditions: Ambient temperature 15–35°C, humidity 45–75%, pressure 86–106 kPa.
6.2.2 Equipment: Constant temperature bath and standard thermometer. Error must not exceed 1/4 of the basic error.
6.2.3 Test points: At least 4 evenly distributed over the scale, including upper and lower limits and 0°C.
6.2.4 Procedure: Insert both thermometers into the bath. Read values after stabilization. Difference is the basic error. At least one test per point in both directions.
6.3 Hysteresis test: Same conditions and equipment as 6.2. Difference between forward and reverse readings is hysteresis.
6.4 Repeatability test: At least three readings at each point. Max difference is repeatability. Must comply with 5.5.
6.5 Thermal stability test: Maintain upper limit for time in Table 6. Temperature must not exceed ±2°C.
6.6 Time constant test: Move from low to high temp, record time when reading reaches 63.2% of step. Must be ≤ 40 s.
6.7 Vibration test: Mount on vibration table, perform vertical vibration as per 5.8.
6.8 Positional impact test: Tilt 90° in all directions, measure indication change.
6.9 Withstand voltage test: Apply 1.5× nominal pressure for 1 min. No damage or leakage.
6.10 Environmental test: Perform high/low temp, impact, and drop tests as per ZBY 002.
7. Inspection Rules
7.1 Factory inspection: Check 5.2 and 5.3 using 6.1 and 6.2. Passed units can be shipped with certificate.
7.2 Type testing required under certain conditions: New products, design changes, periodic checks, long downtime, significant factory results, or national request.
8. Marking and Packaging
8.1 Dial markings: Include manufacturer name, product name, model, unit symbol "°C", accuracy level, serial number, and production date.
8.2 Packaging: Follow ZBY 003 standards.
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