Application and maintenance of Atlas Copco SRTT-B torque sensor

Atlas Copco SRTT-B Static Torque Sensor: Professional Guide to Selection, Operation, and Full Cycle Maintenance

In the field of bolt tightening quality control, the accuracy of torque measurement is directly related to product safety and reliability. The SRTT-B series static reaction force torque sensor launched by Atlas Copco, as an upgrade model of the previous generation of products, provides a more stable and intelligent solution for torque testing with a new mechanical design and built-in storage technology. This article combines official technical documents to systematically review the core features, selection points, installation and operation specifications, accessory configuration, and daily maintenance strategies of SRTT-B from an engineering application perspective, aiming to provide on-site engineers with a practical manual that can be accessed at any time.

Product positioning and core design innovation

SRTT-B belongs to the static reaction force torque sensor, designed specifically for testing torque wrenches (including click wrenches), tightening tools, and measurement scenarios that require avoiding rotational movements. Its typical applications include:

Perform torque verification on pneumatic or electric shut off tools (in conjunction with a mechanical coupling simulator);

Regularly inspect the output accuracy of the tightening gun on the production line;

Standard transmission and calibration comparison in metrology laboratories.

Compared to earlier models, the most significant improvement of SRTT-B lies in the patented new system of the top fixed coupling simulator. The clearance between the sensor and simulator in the old product may introduce measurement errors, but the new design eliminates this clearance through a rigid locking structure, ensuring that there is no gap in the torque transmission path and thus improving repeatability. In addition, the EEPROM chip built into the sensor base can store the identification code, calibration value, sensitivity (2mV/V), pulse number, serial number and the latest calibration date. When connected to Atlas Copco's ACTA series measuring instruments, all parameters will be automatically loaded, completely eliminating the risk of manual input errors.

In depth interpretation of technical specifications

Understanding key technical parameters is a prerequisite for correct selection. SRTT-B covers 11 range models from 0.5 N · m to 2000 N · m, with the following core specifications:

Parameter item specification value

Measurement range: 20% to 100% of rated capacity (ensuring accuracy within this range)

Static accuracy ± 0.5% (percentage of indication, non full scale)

Overload capacity: 125% of rated capacity (overloading is strictly prohibited, otherwise the strain gauge will permanently yield)

Temperature stability 0.1% capacity/10 ℃ (to be used in a constant temperature environment)

Bridge resistance 350 Ω

Working temperature and humidity: 5~40 ℃, 10%~75% RH (no condensation)

Excitation voltage ± 5 VDC (provided by measuring instrument)

It should be noted that 'static accuracy' is only applicable to smooth and impact free loading processes. The document clearly warns that SRTT-B is not suitable for impact tools (such as impact wrenches), as transient pulses can damage internal strain elements. In addition, the principle of "adapter torque superposition" must be followed in practical use - when multiple conversion joints are connected in series, the maximum allowable torque of the entire chain depends on the joint with the smallest rated value and cannot be exceeded.

Model system and selection matching strategy

The naming convention of SRTT-B intuitively reflects the range and drive interface:

Model Capacity (N · m) Drive Method Order Number

SRTT-B 0.5-13 0.5 half "square drive 8059 094 03

SRTT-B 2-13 2 half "square drive 8059 094 09

SRTT-B 5-13 5/2 "square drive 8059 094 15

SRTT-B 10-13 10/2 "square drive 8059 094 21

SRTT-B 25-36 25 36 mm hex 8059 094 28

SRTT-B 50-36 50 36 mm hex 8059 094 36

SRTT-B 100-36 100 36 mm hex 8059 094 45

SRTT-B 250-36 250 36 mm hex 8059 094 64

SRTT-B 500-50 500 50 mm hex 8059 094 63

SRTT-B 1000-50 1000 50 mm hex 8059 094 75

SRTT-B 2000-50 2000 50 mm hex 8059 094 84

The golden rule for selection: The rated capacity of the sensor should be greater than or equal to the maximum output torque of the tested tool, and it is recommended to reserve more than 20% of the margin (because the accuracy guarantee starts from 20% capacity, and if the tool torque is lower than 20% of the sensor range, the accuracy will decrease). For example, when testing a tightening gun with a maximum torque of 800 N · m, the SRTT-B 1000-50 model should be selected instead of the 500 model. At the same time, pay attention to the matching of the drive interface - the small range (≤ 10 N · m) is a half inch square drive, the medium range (25-250) is a 36mm hexagonal drive, and the large range (500~2000) is a 50mm hexagonal drive. If conversion is required, a dedicated adapter (see below) should be used.

Detailed explanation of the entire installation and operation process

4.1 Mechanical fixation requirements

The sensor base is equipped with mounting holes (4 Ø 6.5 through holes for small range, 4 Ø 8.5 for medium range, and 6 Ø 8.5 for large range), which must be firmly fixed to a structure that can withstand reaction torque through bolts. The parallel planes on both sides of the base can also be used for clamping. Loose fixation can lead to measurement drift and even damage to the sensor. The specific external dimensions (A, B, C, etc.) can be found in the mechanical drawings in the document. The weight range is from 1.4 kg (small range) to 10.7 kg (2000 N · m model).

4.2 Tool Connection Method

Square drive model (≤ 10 N · m): Insert the square tenon of the tool directly into the square hole in the center of the sensor, and lock the side lever to fix it.

Hexagonal model (≥ 25 N · m): The top of the sensor has a hexagonal groove, and the corresponding coupling simulator (TJ series) or dedicated adapter needs to be installed before connecting the tool. At this time, the locking lever is located on the side of the sensor body (the document illustration indicates that the lever only exists in hexagonal drive models).

Operation key: Avoid generating lateral force (radial force). When applying torque, the tool axis should strictly coincide with the sensor axis. Tilting or eccentric loading can introduce bending components, seriously contaminating the measurement results.

4.3 Electrical Connection and Data Reading

Connect the sensor and measuring instrument using the standard 19 pin cable:

If using ACTA series instruments, the EEPROM automatically transfers all calibration parameters without the need for manual input.

If a third-party instrument is used, it is necessary to manually input the shunt calibration value (marked on the sensor label) and the number of angle pulses (if angle measurement is required). Attention: The sensor bridge circuit is 350 Ω, and the parallel calibration resistance value is 43.575 k Ω (this is the recommended standard value).

Attachment System and Extended Applications

SRTT-B can be adapted to various mechanical coupling simulators (TJ series) for simulating joints of different hardness to test the automatic shutdown performance of shut off tools. Simulators are divided into two types: "S" (rigid) and "H" (high rigid), corresponding to different tool interfaces:

Simulator model, sensor range, tool interface, rated torque (N · m), order number

TJ SRTT-B S – 0.5 / H – 0.5 0.5 HEX ¼" 0.5 8059 0940 01 / 02

TJ SRTT-B S – 2 / H – 2 2 HEX ¼" 2 8059 0940 03 / 04

TJ SRTT-B S – 10 / H – 10 10 HEX ¼" 10 8059 0940 20 / 21

TJ SRTT-B S-25/H-25 25 25~250 half "square drive 25 8059 0940 07/08

TJ SRTT-B S-500/H-500 500 500~2000 three-quarters "square drive 500 8059 0940 15/16

TJ SRTT-B S-1000/H-1000 1000 1000~2000 1 "square drive 1000/2000 8059 0940 17/18

Attention: The rated torque of the simulator must be equal to or greater than the range of the sensor itself (e.g. SRTT-B 250 cannot be equipped with TJ-25, should be equipped with TJ-250). In addition, there is also the "QAT Accessory adapter" series square drive conversion head, which can convert hexagonal drive sensors into half ", ¼" or 1 "square drives, making it convenient to use wrenches with different interfaces.

Key points of calibration management and maintenance

6.1 Mandatory Requirements for Annual Calibration

The document clearly states that "to maintain accuracy, sensors must be calibrated regularly" and recommends once a year. The sensor label will indicate the latest calibration date and the next calibration date, as well as the calibration source (such as a factory or certified laboratory). The sensitivity, linearity, and other data stored in the internal EEPROM are updated during each calibration. Users should input the actual value on the calibration certificate provided by the original factory (rather than the nominal value on the nameplate) into the third-party instrument.

6.2 Daily Inspection and Fault Avoidance

Overloading is strictly prohibited: Overloading beyond 25% of the rated value will cause strain gauges to yield and sensors to permanently fail. If there is an unexpected overload during testing, it should be sent for inspection immediately.

Environmental protection: Avoid splashing water, high humidity (>75% non condensing), and drastic temperature changes. For every 10 ℃ temperature change, the zero drift can reach 0.1% of the full range.

Electrical interference: Keep away from strong electromagnetic interference sources such as arc welding equipment, otherwise signal noise will mask the true readings.

No user repairable parts inside: any disassembly will automatically invalidate the warranty, and all maintenance must contact Atlas Copco authorized service point.

6.3 Scrapping and Environmental Disposal

The sensor complies with the EU WEEE Directive (2002/96/EC), and its product body and components (including batteries) are marked with a forked trash can symbol. Within the European Union, scrapped equipment must not be mixed with unclassified municipal waste and must be collected and recycled separately in accordance with local regulations to facilitate material reuse and reduce environmental burden.

Typical Problems and Engineering Suggestions

Q1: Can SRTT-B be used to test the impact wrench?

A: Absolutely not allowed. The document clearly warns that it is not suitable for impact tools. The high-frequency pulse of impact load can cause strain gauge fatigue and zero drift, and a dedicated dynamic torque sensor should be selected.

Q2: How to calculate the maximum torque when connecting multiple adapters?

A: Limited to the adapter with the minimum rated torque in the chain. For example, if a rated 500 N · m adapter is connected in series on SRTT-B 1000, the entire system cannot exceed 500 N · m.

Q3: Why is the reading inaccurate when using third-party instruments?

A: It is necessary to confirm that the shunt calibration value and bridge resistance (350 Ω) on the sensor label are correctly inputted, and the excitation voltage is ± 5V. At the same time, check whether the temperature is within the specified range.

Q4: How to determine if the sensor is overloaded or damaged?

A: If there is a sustained deviation, decreased repeatability, or inability to return to zero in the measured values during the calibration cycle, plastic deformation may have occurred. It should be immediately stopped from use and sent for inspection.