1. Scope and Field of Application
This standard outlines the terminology, product classification, technical specifications, testing procedures, inspection rules, labeling, packaging, and other related aspects of industrial bimetal thermometers (hereinafter referred to as thermometers).
It is applicable to temperature sensing components that consist of bimetallic elements and sheaths, featuring a circular dial with a measurement range from -80°C to +500°C.
2. Reference Standards
ZBY 002 – Basic environmental conditions and test methods for instrumentation, transportation, and storage
ZBY 003 – Technical conditions for instrumentation packaging
ZBY 120 – Working conditions for industrial automation instruments – temperature, humidity, and atmospheric pressure
ZBY 122 – Basic types, dimensions, and general technical requirements for the pointer part 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 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.
3.4 Placement 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
b) Axial
c) Universal
d) Angular
The Mechanical and Electronic Industry Department approved this standard on June 12, 1988, and it became effective on January 1, 1989.
4.2 Dial plate nominal diameter – The nominal diameters of the thermometer dials are 60 mm, 100 mm, and 150 mm.
4.3 Measuring range – The measuring range must comply with Table 1.
Table 1:
-80 to +40
-40 to +80
0 to 50
0 to 100
0 to 150
0 to 200
0 to 300
0 to 400
0 to 500
4.4 Accuracy grade – Thermometers have an accuracy rating of 1, 1.5, or (2.5). Note: The accuracy level in parentheses is not recommended.
4.5 Detection element and mounting thread diameter – The detection element and mounting thread must conform to Table 2.
Dial nominal diameter | Detection element diameter | Mounting thread
60 mm | 4 mm | M16 × 1.5
100 mm | 8 mm | M27 × 2
4.6 Insertion length – The insertion length of the thermometer is available in 75, 100, 150, 200, 250, 300, 400, and 500 mm. Note: If longer than 500 mm, it should be agreed upon between the manufacturer and user.
4.7 Jacketed nominal pressure – The jacketed nominal pressure should be selected from the series of 1.0, 1.6, 2.5, 4.0, and 6.4 MPa.
4.8 Installation connection method – The installation and connection method includes: adjustable pipe joint, pipe joint (external thread), pipe joint (internal thread), and fixed thread.
4.9 Indication adjustment mechanism – Thermometers are categorized into three types: no indication adjustment mechanism, external indication adjustment mechanism, and internal indication adjustment mechanism.
5. Technical Requirements
5.1 Normal working conditions – The normal operating conditions must meet the requirements of Table 3.
Table 3:
Workplace temperature (°C) | Relative humidity (%)
Covered area –25 ~ +55 | 5 ~ 100
Outdoor area –40 ~ +85 | 5 ~ 100
Note: Special working conditions are subject to agreement between manufacturer and user.
5.2 Appearance, structure, and assembly quality – The appearance, structure, and assembly quality must meet the following:
a) No rust on parts; protective layer must be firm, uniform, and smooth.
b) Glass or transparent material must be clear and free of defects affecting reading.
c) Type, basic parameters, and dimensions (with tolerances per manufacturer’s regulations) must conform to Chapter 4.
d) Pointer and dial must meet ZBY122 and ZBY123. Pointer length (from center of rotation to tip) must match Table 4. Distance between indicator portion and dial plane must not exceed 5 mm.
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 conform to Table 5.
Table 5:
Accuracy level | Basic error (%)
1.0 | ±1.0 of the range
1.5 | ±1.5 of the range
(2.5) | ±2.5 of the range
5.4 Hysteresis – Must not exceed the absolute value of the basic error limit.
5.5 Repeatability – Must not exceed half of the absolute value of the basic error limit.
5.6 Thermal stability – After maintaining the upper measurement limit for the time specified in Table 6, the detection element must meet the requirements of 5.3.
Table 6:
Measuring upper limit (°C) | Holding time (h)
≤300 | 24
400 | 12
500 | 4
5.7 Time constant – Must not exceed 40 seconds.
5.8 Vibration resistance – Must withstand 25 Hz frequency, 0.6 mm displacement amplitude, sine wave vibration for 24 hours. After testing, it must still meet 5.3 and show no mechanical damage.
5.9 Position influence – Tilting the thermometer 90° forward, backward, left, or right from the reference position must not cause an indication change exceeding the absolute value of the basic error limit.
5.10 Pressure-resistant jacket – Must withstand 1.5 times the nominal pressure without damage or leakage.
5.11 Transportation, storage, and environmental conditions – Factory-packed thermometers must withstand high temperature (+55°C), low temperature (-40°C), continuous impact (98 m/s², 11 ms pulse), and free fall (250 mm) tests as per ZBY002. They must still comply with 5.2, 5.3, 5.4, and 5.5 after testing.
6. Test Methods
6.1 Visual and tool inspection for appearance, structure, and assembly quality as per 5.2.
6.2 Basic error limit test – Conditions: ambient temperature 15–35°C, relative humidity 45–75%, atmospheric pressure 86–106 kPa. Test equipment: constant temperature bath; standard instrument: standard thermometer. Measurement error must not exceed 1/4 of the basic error limit.
6.3 Hysteresis test – Same conditions, equipment, and points as 6.2, excluding upper and lower limits. Difference between forward and reverse readings is hysteresis, which must meet 5.4.
6.4 Repeatability test – Same conditions, equipment, and points as 6.2. Readings at least three times per point. Maximum difference is repeatability, which must meet 5.5 and also comply with 5.3 and 5.4.
6.5 Thermal stability test – Insert detection element into thermostat, maintain upper limit for time in Table 6. Temperature must not exceed ±2°C. After test, must meet 5.6.
6.6 Time constant test – Insert detection element into cold medium, stabilize, then quickly move to hot medium (difference >50% of range). Record time when indication reaches 63.2% of temperature step. Must meet 5.7.
6.7 Vibration resistance test – Mount thermometer on vibration table, align dial parallel to gravity. Apply vertical vibration as per 5.8.
6.8 Positional impact test – Tilt thermometer 90° from reference position, measure indication change.
6.9 Withstand voltage test – Apply 1.5× nominal pressure at room temperature for 1 minute. No damage or leakage.
6.10 Environmental conditions test – As per ZBY002 and 5.11.
7. Inspection Rules
7.1 Factory inspection – Each thermometer must be tested according to 5.2 and 5.3, using 6.1 and 6.2. Passed units can be shipped with a certificate.
7.2 Type testing – Required under the following conditions: new product trial production, major design changes, periodic testing during production, resumption after long downtime, significant factory inspection differences, or national agency request.
8. Marking and Packaging
8.1 Dial markings – Include: manufacturer name, product name, model number, unit symbol “°Câ€, accuracy level, product number, and manufacturing date.
8.2 Packaging – Must follow ZBY003 standards.
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