Posts Tagged ‘pressure transmitter’

RFID Technology Streamlines Process for Mandatory Hydraulic Inspection

Tuesday, April 12th, 2016

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OEM Transmitters : All-inclusive

Tuesday, July 8th, 2014

By Daniel Hofer, Dipl.EL.-Ing FH and Bernhard Vetterli, Dipl, Dipl.El.-Ing.HTL

Miniaturization in pressure measurement technology

Keller’s OEM transmitters are systems that can be described as “embedded” in the best sense of the word – and in two different ways. First the sensor and the downstream electronics are embedded in the same housing. And second, the transmitter capsules themselves are ideally suited for embedding in application-specific systems. Depending on requirements, the output signal is standardized and temperature-compensated (ratiometric or digital).

Thanks to Chip-in-Oil (CiO) technology developed at Keller, the trend toward sensor miniaturization is now a reality. This development can offer impressive advantages: an extremely compact structural design, high resistance to electrical noise fields, and high vibration resistance thanks to low mass and short conduction paths.

To put it clearly, CiO technology means that an ASIC is fitted directly next to the pressure sensor – in the same housing – to provide users with a whole range of beneficial functions. However, this does not make the pressure measurement capsule any larger;  Its external dimensions remain the same. This transmitter concept is available in housings 4L…9L, starting from a diameter of 11mm.

Sintered-in pressure-resistant glass lead-throughs feed the transmitter signals outward. The internal Wiring uses short, lightweight bonding wires – with the total exclusion of air in oil. First, this approach eliminates the need to connect filigree signal processing boards with multi-wire cabling in the rest of the installation process for the pressure transducer. And second, there is no need to protect the downstream electronics against moisture and condensation.

Together with the high-grade steel housing, the glass lead –throughs act as feed through capacitors, forming a Faraday cage. This makes the CiO technology extremely resilient to electrical fields. Even field strengths of 250V/m at frequencies of up to 4GHz are unable to influence the measurement signal. The digital interface must be protected by the equipment manufacturer itself.

The ASIC is designed as a microcontroller with the corresponding peripherals, so the sensor signals can be registered with high resolution and dynamism. In addition to the process pressure as such, the temperature of the pressure sensor is measured and is used for mathematical compensation when the signal is processed.

OEM transmitters supply two signals: a ratiometric analog voltage output and a digital inter-integrated circuit interface (12C).

Ratiometric output signal

The secret of the ratiometric format to the output signal is that it actually has no format at all, because it depends on the voltage supplied. This is an inestimable advantage for applications in integrated systems. If the analog-to-digital converter downstream of the transmitter is operated with the same supply voltage, the digital measured value will always be correct. This is because the height if the digitization steps depend on the voltage supply, but the number of steps does not – and their number is the critical factor. Using ratiometric signals substantially reduces the outlay on passing signals from the pressure transmitter to the A/D converter in the downstream electronics, and calibration steps are unnecessary; in the specific case of connection to a microcontroller with an integrated A/D converter, this outlay equals zero. Nevertheless, an interval is specified for the output signal, i.e. 0.5…4.5V for s supply voltage of 5.0V. With a stable and precise supply voltage, this interval can also be used directly as the “standard signal.” The sampling rate of 2 kHz offers amazingly good dynamic scope for a product based on the AD/DA principal. Moreover, the embedded electronics in CiO technology provide constant protection against overvoltage and polarity reversal on all lines up to ±33 VDC.

Embedded interface I2C

OEM transmitters that are the same size as pressure measurement capsules are never connected directly to field bus systems. Instead, the respective coupling modules have corresponding input interfaces, e.g. for the inter-integrated circuit or I2C interface. For years, this has been the serial standard to cope with short distances in embedded systems. The I2C master needs two lines for the serial data and the pulse (clock) for synchronous sampling. Consequently, no timing requirements are specified for the master – which, in fact, determines the timing. Each OEM transmitter has its own address, which is addressed by the I2C master. In the existing configuration, one master could manage 128 different addresses. The pressure and temperature values are registered by means of a request from the master, and are then available at the transmitters (slaves) after less than 10ms, so that they can be clocked out according to a specified protocol. The values are temperature compensated and standardized, and they only need to be scaled from the 15-bit integer to a pressure and/or temperature with units.

Mobile Application

Unlike the CiO version with the ratiometric output, CiO versions with I2C output can operate with a voltage supply of only 1.8…3.6 VDC, so they are excellently prepared for mobile battery-powered applications. In this case, however, features also include the short conversion time of less than 10ms (during which a mere 1.5mA is drawn) and the excellently optimized Sleep mode: unless they are polled, the transmitters remain in this mode, which is typically specified as 0.1µA. If the master allows suitable fast communication, 100 samples per second can be therefore be attained.

OEM transmitters for Everyone

Typical key data vary according to the format of the output signal – ratiometric or digital. With an analog output, the transmitter can be used at temperatures between -40°C and +150°C, whereas the I2C output is subject to an upper limit of 80°C. The pressure range for the analog version extends from 2 bar to 1000 bar; for the digital version, the range is from 2bar to 200 bar. For a greater dynamic scope with increased power consumption up to a maximum of 8mA, the analog version should be chosen. For low voltage and low power applications, the digital version (which also provides temperature information) is recommended.


Keller’s C-series OEM transmitters herald a new chapter in the history of high-integration pressure measurement technology. The Chip-in-Oil concept moves signal processing directly into the protective oil-filled pressure measurement capsule housing, made of stainless steel. Linearization, temperature compensation and parameterization are handles here. For integration into higher-level systems or battery-powered devices, versions are available with ratiometric voltage output or with a serial-digital I2C interface. Various structural designs can be supplied depending on the specific application.

The M5 series – New from Keller

Tuesday, July 1st, 2014

KELLER  is again setting new standards with the M5 series. All in all, the new sensor for static and highly dynamic measurements (up to 50 kHz) represents something totally unique with an operating temperature range up to 180 °C, ±0,1 %FS , miniature size (M5 connection), and the remote signal conditioned 0…10VDC output option.

Ingenious design brings multiple benefits

The key to measuring highly dynamic pressure variance is to achieve the most direct connection possible between sensor element and medium. With this in mind, KELLER has come up with a micro-mechanical solution without media isolation diaphragm, capillary tubing, sealants, or adhesives. In the M5 series, the rear of the silicon sensor is soldered to a supporting element designed for excellent fluid dynamics, which in turn is secured flush at the front of the pressure connection.

This sophisticated design enables dynamic measurements with a bandwidth of 0…50 kHz and offers a number of additional benefits including excellent decoupling of mounting forces and structure-borne vibration, extensive media compatibility, and the durability offered by the anti-oxidation coatings. Other impressive features of the M5 series are its overpressure protection of up to five times the measurement range and its pressure connection with an external thread of just Ø 5 mm for installations in space-limited locations.

Separation of sensor and signal converter

The pressure sensors in the M5 series are intended for operating temperatures between -40 °C and +180 °C with a narrow total error band (i.e. including temperature errors) of ±1%. Without the remote signal converter, they come with a typical output signal range of 80 mV (based on a 1 mA supply) and an individual calibration certificate. The 3 bar, 10 bar and 30 bar measurement ranges are available for absolute pressure measurements. Separating the pressure sensor and the signal converter enables measurements at close proximity, even in units installed in cramped conditions and exposed to high temperatures.

 A top-class signal converter

To avoid any reduction in the piezoresistive pressure sensor’s broad dynamic range of 50 kHz, the KELLER has opted not to digitize the measurement signal to be produced. Instead, the purely analogue signal path is adjusted in real time via the compensation electronics, which are fully controlled by a microprocessor. This ensures the output signal, amplified to 0…10 V, retains the full dynamic range of the sensor signal. The measurement system, consisting of the pressure sensor and signal converter, undergoes an end-to-end calibration at the factory once the customer-specific parameters have been determined. In addition, the operating temperature range of -40 to +125 °C for the remote electronics satisfies the exceptional demands required by engine test benches, for instance.

Series M5 HB

Ideal for measurements at close proximity on engine test benches and in wind tunnels

The thermally ultra-robust pressure transducers in the KELLER M5 series support high-precision static and dynamic measurements up to a bandwidth of 50 kHz and at working temperatures of up to 200 °C at the pressure sensor. With its M5 connection thread, the remote pressure sensor – which contains no oil and associated isolation diaphragm and no sealant or adhesive in contact with the media – is ideal for taking highly dynamic measurements at close proximity. It can even do this at the very thin pipes used in engine test benches, in wind tunnels or during turbine blade tests.

New from Keller – PRD-33X differential pressure transmitter for closed tank level measurement

Tuesday, October 22nd, 2013


The Series PRD-33 X was developed for applications that require a high accuracy differential pressure measurement together with high overload resistance in differential pressure ranges as low as 350 mbar.

The Series PRD-33 X is the result of ongoing development of the KELLER PD-33 X differential pressure transmitters. Thanks to a second integrated pressure sensor, the line, or common mode, pressure can now be measured along with the differential pressure, resulting in several notable features not found in traditional differential pressure transmitters.


– High-accuracy differential pressure measurement with compensated line pressure       dependency

– Differential pressure range from 350 mbar to 3 bar

– Pressure- and temperature-compensated

– Signal output: ΔP, base pressure, and temperature

– High overload resistance: ± 35 bar also in the 0…350 mbar measuring range

– Configurable via RS485 interface incl. software-manager for online data control, data save and programming

– Compact structural design including various electrical connections (binder, cable, M12)


– Level measurement of technical gases in liquefied gas tanks
– Differential pressure measurement in case of high unilateral overload resistance

Level measurement of pressurized tanks

Level measurement for non-pressurized tanks is a common application, and can easily be accomplished through the use of a “traditional,” relative-type level or pressure transmitter. The reason is that there is no pressure differential between the ullage pressure and barometric pressure. However, pressurized tanks present additional challenges.

In closed-system and pressurized tanks, two measurements must be made to calculate media level. Commonly, this is accomplished by using two separate pressure transmitters; one to measure tank pressure (liquid + ullage = P1), and one to measure ullage pressure (P2). Liquid level is then calculated by subtracting the ullage pressure value (P1-P2). Keller differential pressure transmitters make it possible to simplify the process with one instrument, as shown below:


Figure 1
Figure 1

In these more traditional applications, a standard differential pressure transmitter would prove adequate, however, other closed tank level applications, such as cryogenic storage tanks, require special transmitter capabilities.

Industrial Gas / Cold-converter systems / Cryogenics storage tanks

Cold storage and cryogenic tanks allow a large amount to be stored economically in a small space. However, the combination of low temperatures and precise level control requirements make standard differential pressure measurement increasingly difficult.


Figure 2
Figure 2

For example, during gas withdrawal the temperature and the pressure decrease. If the pressure drops below a defined threshold, liquefied gas is passed into a conduit outside of the insulation, where it is heated and vaporized, which will increase pressure. If too little or no gas is drawn, the inner pressure rises by taking in heat from the outside. If the upper threshold pressure is reached, gas is discharged into the environment which lowers the temperature and internal pressure. The logistics for these tanks is essential, and thus a continuous level monitoring is required.

Since the tanks are pressurized, the level measurement is more complex, as not only the liquefied gas column, but also the internal pressure needs to be measured to determine the liquid level. Additionally, varying tank size creates additional difficulties, as smaller tanks (< 3m) have particularly high requirements, since the pressure differential can be as low as 200 mbar (FS) with base pressure as high as 32 bar. When filling and manipulating the valves, the tank pressure may exert onesided on the differential pressure transmitter, while the air pressure is exerted on the other side. That‘s why a onesided overload of 32 bar is required.

Keller Differential Pressure Transmitter Comparison

Product Comparison

Differential pressure measurement provides a streamlined process for efficiently monitoring liquid levels in closed and pressurized tanks. As a world leader in level and pressure measurement instrumentation, Keller differential pressure transmitters are proven to provide outstanding accuracy and versatility to your changing needs.

Introducing the LEO 5

Wednesday, June 26th, 2013

Keller is pleased to announce the new LEO 5 digital pressure gauge. It is the first Keller gauge to incorporate a stainless steel housing, safety glass face, rechargeable accumulator power supply, and capacitive-touch controls. Plus, the back lit LCD display ensures readability in any lighting condition.

This new instrument combines Keller’s proven piezoresistive measurement capability with enhanced microprocessor circuitry to deliver outstanding accuracy, and maximum capability.  The unique combination provides 2 measurement modes: Standard for high resolution pressure measurement and Peak for 16 bit resolution at a rate of 5kHz.

The LEO 5 also provides an integral data logger; storing pressure, temperature, and time/date. This interfaces with a PC for data retrieval, device configuration, firmware updates, and accumulator recharge.

Several options are available to ensure compatibility with a variety of applications in new or existing systems. For more information call 877-253-5537, emails, or visit