HBKShop | Training | Resources

arrow_back_ios

Main Menu

See All Products See All ナレッジ See All ソリューション See All サービス＆サポート See All HBKについて See All お問い合わせ
arrow_back_ios

Main Menu

See All Acoustic End-of-Line Test Systems See All DAQ および機器 See All エレクトロ音響アプリケーション See All Software See All Sensors See All Vibration Testing Equipment See All リソースセンター See All アプリケーション See All 各産業 See All インサイト See All サービス See All サポート See All 当社の事業 See All 私たちの歴史 See All サステナビリティ（持続可能性） See All グローバルな事業展開
arrow_back_ios

Main Menu

See All Actuators See All Combustion Engines See All Durability See All eDrive See All Transmission Gearboxes See All Turbo Charger See All DAQシステム S&V See All 高精度校正システム See All 産業用電子機器 See All パワーアナライザ See All S&V ハンドヘルドデバイス See All DAQ systems See All Wireless DAQ system See All Pinnae See All エレクトロ音響アプリケーション用アクセサリ See All DAQ See All Drivers API See All nCode - Durability and Fatigue Analysis See All ReliaSoft - Reliability Analysis and Management See All Test Data Management See All Utility See All Vibration Control See All Inertial Sensor Software See All Acoustic See All Current / voltage See All Displacement See All Force See All Inertial Sensors See All ロードセル See All Pressure See All Strain See All Torque See All Vibration See All 測定加振器 See All Smart Sensors with IO-Link interface See All LDS シェーカーシステム See All パワーアンプ See All 振動コントローラ See All 音響 See All 設備とプロセスの監視 See All カスタムセンサ See All データの取得と分析 See All 耐久性および疲労 See All Electric Power Testing（電力テスト） See All NVH See All 信頼性 See All スマートセンサ See All 振動 See All 計量 See All 自動車および地上輸送 See All 校正 See All インストール、メンテナンス、修理 See All サポート ：ブリュエル・ケアー製品 See All Release Notes See All コンプライアンス (Compliance) See All Our People
arrow_back_ios

Main Menu

See All CANHEAD See All GenHS See All LAN-XI See All MGCplus See All Optical Interrogators See All Fusion-LN See All SomatXR See All CCLD （ IEPE ）信号コンディショナ See All 産業用電子機器用アクセサリ See All ハンドヘルドソフトウェア See All S&V ハンドヘルドデバイス用のアクセサリ See All Wireless Gateways See All Wireless Nodes See All BK Connect / PULSE See All API See All Microphone sets See All Cartridges See All 特殊マイク See All 音響キャリブレーター See All マイクロスコーププリアンプ See All 音源 See All 音響トランスデューサ用アクセサリ See All Accessories See All デジタルロードセル See All ロードセル用アクセサリ See All 実験 See All トランスデューサ製造（ OEM ） See All ひずみゲージ用アクセサリ See All 回転タイプ See All ピエゾ式 CCLD (IEPE) 加速度計 See All ピエゾ式加速度計 See All Impulse hammers / impedance heads See All ケーブル See All Accessories See All Accessories See All パワーアンプ See All 振動試験装置用アクセサリ See All 電気音響 See All 音源探査（Noise source identification, NSI） See All 環境騒音 See All 音響パワーと音圧 See All 騒音認証 See All 産業用プロセスコントロール See All 構造ヘルスモニタリング See All 電気デバイス試験 See All 電気システム試験 See All グリッド試験 See All 高電圧試験 See All 導電加振機による振動試験 See All 構造力学 See All 機械分析と診断 See All プロセス計量 See All 車両の電動化 See All トランスデューサの校正サービス See All ハンドヘルド測定器の校正サービス See All 機器およびDAQの校正サービス See All 現地での校正 See All リソース See All ソフトウェアライセンス管理

Measuring press forces: accurate, cost effective and reliable

Press force is a crucial parameter for monitoring, quality assurance and force control in presses. As requirements in these areas continue to rise, press force measurement has become increasingly important and is now a standard practice.
SLH700-7920 hbk

How to measure press force

In general, there are two primary methods for measuring forces in pressing processes:

1.      Direct force measurement

This method involves installing a force transducer i directly in the path of the force withing the pressing machine. Typical sensors used include the C6b sensors and, in some cases, the high precision force transducers U10M or U10F. This approach allows for the most accurate force measurements, as these sensors come pre-calibrated,  enabling immediate measurements without the need for on-site calibration.

Press forces can be very high, reaching up to the Meganewton range. While HBK offers force sensors capable of handling these high forces, it’s important to note that these models can be quite heavy, sometimes exceeding 100 kg, and their installation requires significant effort.

for C6B 2MN 01
for U10F 250kN 03

Typical sensors used include the C6b sensors and, in some cases, the high precision force transducers U10M or U10F

2.      Indirect force measurement

Indirect fore measurements are performed by using strain gauges or so-called strain links, or extensometers, such as the SLH700 series from HBK.

str_SLH700-7920_NoBG

The press force is transferred through machine frame, causing strain on the surface of the force leading [SC1] machine parts. In many cases, this strain is linearly related to the press force. Strain links are installed at suitable locations on the press, converting the strain into a measurable voltage signal. This principle has been known for decades and used in thousands of applications.

If the goal is to measure the force in Newtons or another unit, calibration is required after mounting the strain link. This involves substituting the pressing tool and/or workpiece with a reference sensor. Force is then applied to the setup, and the output signals from both the reference force transducer and the strain link are measured in parallel. This process must be performed for at least one force, though it is common practice to use several load steps and repeat the calibration.  By considering  the force measurement and the strain link output, the sensitivity of the strain link can be calculated, enabling force measurement in Newtons using an extensometer.

Mounting strain gauges is easy, as the devices are installed with just two M6 screws on the press. It is important to remove any paint and ensure the surface is grease-free. However, since the required force for an SLH strain link is low (just 600 N for a strain of 500 µm/m), the preparation requirements for the measurement point are minimal.

The optimal mounting locations can vary depending on the specific case. See examples in the pictures below.

While strain links may not offer the same precision as force transducers, they come with several advantages:

  • Since there is no sensor in the force path,  the stiffness and dynamic characteristics of the press remain unchanged
  • The cost of force sensors in the Meganewton range significantly higher compare to strain links, making press monitoring with strain links much more economical
  • Installing strain links is much simpler
     

Passive or active strain links?

Strain links are available as passive strain gauge-based sensors, which require an amplifier module to amplify the small output signal and provide a usable signal to the control system.

There are also extensometers with built in amplifiers, eliminating the need for an external amplifier module. Which version is suitable in which situation?

When using a single strain link, models with built-in amplifiers are generally more cost effective and provide a more reliable output signal (current or voltage output instead of mV/V signal).

In many cases, strain links are connected both electrically and mechanically in a parallel mounting configuration. This setup is often used to minimise the influence of bending on the measurement result.

In case of pure tensile or compressive strain, both sensors in the example above measure the same strain in the same direction. If bending occurs, one element measures positive strain while the other element measures negative strain. This results in a zero output, achieving bending moment compensation.

It is also possible to use four sensors from the SLH series and connect them in parallel. However, a parallel setup is much easier with non-amplified extensometers and an external amplifier. The passive SLH are designed for this measurement situation: their high input resistance of 1000 Ohms allows for the connection of four or more sensors in parallel without issues related to low sensor impedance with standard market instruments. Additionally, the sensors are adjusted for the relationship between output resistance and rated output, which is important for parallel setups.
 

Teach-in procedure with amplifier extensometers of the SLH series

Many available strain transducers with an integrated amplifier module only have a fixed amplification. For example, 500 µm/m corresponds to an output signal of 10 V. The fundamental drawback of this method is that the maximum output signal depends upon the given amplification, which cannot be changed. If, a strain of 200 µm/m is used as the input signal, the resulting output voltage is 4 V. This can lead to unsatisfactory results, if the next element in the measurement chain is a module that has a low resolution or increased noise.

SLH700VA strain links with integrated amplifier electronics overcome this problem by providing the maximum possible output signal at all times, regardless of the intended purpose.

The teach-in procedure is simple:

  • Install the sensor as usual and reduce the load on the machine (press, roll stand, silo) to zero. Send a longer pulse to the teach-in input to allow the electronics to memorise the zero point
  • Apply the calibration load and send a short pulse to the teach-in input. This adjusts the electronics  between the zero point and the calibration load
  • This process ensures that the input range of the next level is fully utilised at all times
  • The teach-in procedure can be performed at 25%, 50%, or 100% of the full scale

Additional advantages of this procedure:

  • There is always a 10% buffer in the upper and lower parts of the measuring range. Higher strain signals, such as those occurring during a failure, failure) are still amplified and transmitted
  • The characteristic curve can be negative, allowing both elongation and shortening to be converted into a positive signal
  • The built-in measuring amplifier provides low noise and a bandwidth of 2 kHz
  • It is essential to permanently store the span, which is the difference between the minimum and maximum values. Therefore, resetting to zero after a power failure is imperative
     

Why choose SLH extensometers?

SLH sensors offer a cost effective and reliable alternative to load cells for press force measurement with load cells. Here are some key benefits:

  • With an IP68 protection rating, the sensors and cables are resistant to most oils and water, and can be used on drag chains All materials are rust free, ensuring reliable measurements in harsh industrial environments
  • The low force shunt means that the sensor’s influence on the press is negligible.
  • Mounting requires just two screws and no special tools
  • Users can choose between amplified and passive versions depending on the measurement situation. Both models have the same outer dimensions, allowing for easy exchange
  • The amplified version supports partial teach-in functionality, making it suitable for situations where applying the full range force is not possible, such as in dynamic presses

Related Products