The pressure transmitters of the 7LD series use the chip-in-oil technology developed by KELLER, uniting a pressure measuring cell, digital temperature compensation and signal processing in a compact housing made of stainless steel or Hastelloy. The transmitters are extremely resistant to environmental influences and delivery highly accurate measurement results as a digital output signal. The I2C interface and the low supply voltages make it easy to integrate in microcontroller-based systems. The extremely low power consumption is ideal for battery-operated devices. The D line is perfect for IoT solutions.
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 transmitter. 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.
For example, compensation for line pressure effect is now accomplished during factory calibration. Moreover, both differential and line (absolute) pressure may be read by the user. In addition, the PRD-33 X features high differential overload resistance; e.g., ± 35 bar with a differential measuring range of only 350 mbar (100:1).
The internal differential pressure sensor element is isolated from the High (+) side media by a compliant stainless steel diaphragm, while the Low (-) side media impinges directly on the back side of the silicon measuring cell. Also isolated from the High (+) side media is the line (absolute) pressure sensor. The floating sensor assembly guarantees maximum decoupling from external mechanical forces.
Another notable feature of the Series PRD-33 X is the robust digital RS485 bi-directional communication interface. Information such as serial number, pressure range, filter settings and process values for both differential and line (absolute) pressures and their temperatures are easily obtained.
This combination of features enables certain measurements not possible with traditional differential pressure transmitters. For example, filling levels in liquefied gas storage tanks, including oxygen, nitrogen, carbon dioxide and argon can now be measured safely, accurately and at reasonable cost.
The low-cost OEM pressure transducers of the 6S series are based on a piezoresistive measuring cell with a brazed metal diaphragm in a steel housing.
The Series PD-39 X does not measure the differential pressure directly – instead, it uses two absolute pressure sensors to take the measurement indirectly. As well as reducing costs, this differential pressure transmitter is also more robust in relation to unbalanced (one-sided) overloading. The differential pressure range should be at least 5% of the standard pressure range. Each pressure side has two pressure connections, so the
Pressure measurements can be displayed and recorded on PC or Laptop with help of the software ControlCenterSeries30 (CCS30) and a seriel interface cable. Export of recordings to usual file formats possible. Up to 128 devices can be connected together into a KELLER Bus-system.
The Series PD-39 X does not measure the differential pressure directly - instead, it uses two absolute pressure sensors to take the measurement indirectly. As well as reducing costs, this differential pressure transmitter is also more robust in relation to unbalanced (one-sided) overloading. The differential pressure range should be at least 5% of the standard pressure range. Each pressure side has two pressure connections, so the PD-39 X is easy to use in pressure lines
So that the differential pressure can also be measured exactly if the standard pressure range/ differential pressure ratio is high, this series also features the tried-and-tested microprocessorbased technology that is used in Series 30 X. All reproducible pressure sensor errors (i.e. nonlinearities and temperature dependencies) are entirely eliminated thanks to mathematical error compensation. The sensor signals are measured with a 16-bit A/D converter, so the individual standard pressure ranges can be measured to an accuracy of 0,05%FS throughout the entire pressure and temperature range.
The transmitters have a bus-compatible two-wire RS485 half-duplex interface which is modelled on the ”MODBUS RTU”. KELLER offers interface converters to RS232 or USB for use here. The READ30/PROG30 program and the protocol are freely available. The interface offers these capabilities:
- Readout of pressure and temperature values for both sensors. This allows readout of the diffe- rential pressure as well as the two standard pressure ranges.
- Calibration of zero points and amplification.
- Scaling of the analog output to different pressure ranges or units.
- Configuration settings such as measurement rate, low-pass (LP) filter, bus address, etc.
- Readout of information such as serial number, compensated pressure and temperature ranges, etc.
The analog output is freely scalable via the interface. For flow measurements, the root of the differential pressure can also be outputted. The calculated value can be outputted via an analog interface (0…10 V or 4…20 mA).
The high-accuracy LEO-Record-Ei digital manometers can record pressure and temperature autonomously for long periods thanks to their memory function. The data logger can be connected to a computer via the RS485 interface for configuration and for reading out the recorded data. The current pressure value can be displayed in a wide variety of units of pressure. Power is supplied by a high-quality 3,6 V lithium battery.
Intrinsically safe – suitable for use in explosive atmospheres.
Series 22 DT was developed and homologated specially for use in so-called "bivalent" vehicles fitted with engines for combined natural gas/gasoline operation. The unconventional design with a small mass swept by the flow results in a fast response with temperature changes, the temperature being measured by an NTC or PT sensor located directly behind the stainless steel separating diaphragm. The same diaphragm transmits pressure via a capillary to a stress-free mounted silicon measuring cell.
The signal processing for pressure and temperature is carried out by an electronic module connected to the sensors by flexible conductors. Mounted to the back of the electronic module, which is directly connected to the 6-pole plug connector are the EMC protection components. A special feature is the immunity from interference from electromagnetic fields up to 200 V/m.
The pressure transducers of the 9L series have a compact, robust housing made of stainless steel, giving them outstanding long-term stability for a range of OEM applications. The metal diaphragm is welded on front-flush and gap-free, separating off the piezoresistive pressure sensor, which is made of silicon, from the measuring medium. Every pressure transducer is measured over the entire pressure and temperature profile and is supplied with a detailed calibration sheet
The Series 41 X combines the ceramic measurement cell for low pressure ranges with the µP electronics of the digital Series 30 transmitter. The pressure values from the signals of the pressure and temperature sensors are determined by polynomial compensation (see reverse). The values can be displayed and stored on a PC via an RS485 interface and programming can also be carried out.
The transmitters are calibrated to the base range. The PROG30 software permits programming of the analog output signal in each section of the range within the base range (e.g. range 100 mbar. Output 4…20 mA for 20…60 mbar).
With KELLER RS converters K-100 Series, up to 128 transmitters can be hooked together into a bus system and read by means of a PC or laptop. READ30 software allows the current pressure of each transmitter to be read or the pressure activity of several transmitters to be recorded or stored whilst “on line”.
Series 22 offers a reliable cost effective solution for customers requiring medium to high quantities, of mass produced transmitters. Utilising the KELLER automatic brazing lines, this new technology allows crevice-free construction of the pressure port with no internal seals or O-rings, making possible high volumes at low cost.
In the brass 22 M, a steel insert and a nickel diaphragm are brazed into a brass housing. In the steel 22 S, all parts are stainless steel (AISI 316 L). The glass feed-through header and silicon pressure sensor are welded to the steel insert underneath the oil filling.
The electronic circuit is fitted to the Packard plug. EMC-protection-components are mounted on the plug side, the amplifier on the sensor side. A flexible printed circuit “TAB” connects the sensor with the electronics. The transmitters are designed to have exceptionally good EMC ratings and operate over a wide temperature band, ideal for automotive, hydraulic and refrigeration control applications
Digital Output of Transmitter:
This high precision of 0,01 %FS is available as an option (the standard Series 33 X has an accuracy of 0,05 %FS). These Series are based on the stable, floating piezoresisitive transducer and the newly developed XEMICS micro-processor with integrated 16 bit A/D converter. Temperature dependencies and non-linearities of the sensor are mathematically compensated.
Transmitter with Analog Output:
Integrated in the XEMICS processor is a D/A converter of 16 bit for analog signal outputs of 4…20 mA or 0…10 V. The output rate is 400 Hz. The accuracy is diminished by this converting process by 0,05 %FS. The digital output is available on all transmitters with analog output.
With the KELLER software READ30 and PROG 30, a RS485 converter (i.e. K102 or K107 from KELLER) and a PC, the pressure can be displayed, the units changed, a new gain or zero set. The analog output can be set to any range within the compensated range.
Accuracy and Precision
“Accuracy” is an absolute term, “Precision” a relative term. Dead weight testers are primary standards for pressure, where the pressure is defined by the primary values of mass, length and time. Highest class primary standards in national laboratories indicate the uncertainty of their pressure references with 70 to 90 ppM or close to 0,01%. Commercial dead weight testers as used in our facilities to calibrate the transmitters indicate an uncertainty or accuracy of 0,025%. Below these levels, KELLER use the expression “Precision” as the ability of a pressure transmitter to be at each pressure point within 0.01 %FS relative to these commercial standards. The transmitter’s full-scale output can be set up to match any standard of your choice by correcting the gain with the PROG30 software.
The pressure transducers of the PD-10L series have been developed to measure differential pressure. These OEM pressure transducers have a single silicon diaphragm in their interior, which is pressurised from both sides and measures the pressure difference directly. This design enables them to measure tiny pressure differences even at an extremely high line pressure.
Technology: The Y-line transmitters have an extremely small temperature error. This is achieved using an additional circuit containing a temperature sensor that subdivides the temperature range into fields that are 1,5 Kelvin (K) wide. The TK zero and TK compensation values are calculated for each field and programmed into the additional circuit. During operation, these values are fed into the analogue signal path depending on the temperature. Each temperature is the „calibration temperature” for this transmitter. The accuracy thereof is mainly determined by linearity. 120 fields are available, representing a possible temperature range of 180 K. The wider the temperature range, the greater the amount of testing that is needed to minimise the inaccuracy of the mathematical model.
Flexibility: The extent of the vertical range of manufacture, the modular design and the programmable electronics make it possible to manufacture large, customer-specific batches. The pressure sensors (insulated measuring cells) are manufactured in large quantities and kept in stock. These are then welded into the required transmitter head, equipped with electronics and calibrated over the entire temperature and pressure range in systems with up to 1000 measuring stations. mPm connectors, M12 connectors, Packard connectors and cable connections are used as standard for the electrical connection. In the relative pressure version, the ambient pressure is led into the interior via cable or connector.
Outputs: A 2-wire (4…20 mA) or 3-wire version with voltage output is available as an output signal. For a ratiometric 0,5 to 4,5 V version, we refer to the KELLER Series 21 C product range.
EMC: The 21 Y product line is outstanding due to its extreme ruggedness towards electromagnetic fields. The limits of the CE standard are undercut by a factor of up to 10 with conducted and radiated fields. These transmitters are also extremely immune to external voltages between the housing and the electrical connection, which is particularly important when frequency converters are being used. The high insulation voltage of 300 V make this product ideal for use in the harshest of environments.
Piezoresistive pressure transmitter for applications in bio-reactors or autoclaves. The transmitter is compensated up to 150 °C and may be operated continuously or sterilised at this level, including the special circuit electronics
The transmitters are supplied in absolute or gauge versions, with current or voltage output.
The sensing component is a micro-machined silicon pressure chip of high sensitivity. An independent temperature sensor is integrated on the surface of the silicon chip
The compact LEO2-Ei digital manometers are budget-friendly and provide high accuracy. The minimum or maximum value since the last reset can be displayed at the same time as the current pressure value in a wide variety of units of pressure. The swivel adapter allows the device to be optimally positioned. Power is supplied by a conventional CR2430 coin cell battery (provided).
Ultramodern welding techniques and advances in the miniaturization of electronic circuits now make it possible to manufacture a pre-insulated, piezoresistive micro-transmitter with properties that were no more than a dream 10 years ago.
The circuit is based on the PromComp principle which KELLER offered in a separate version as a laboratory device 20 years ago when it attained accuracy of 0,1 %FS over a temperature range of 100 K. In those days the electronic circuitry was the size of a cigar box, but now it can be accommodated on a print that is a mere 12 mm in diameter.
Although this digital component is only slightly more expensive to produce than an analog circuit, it allows a piezoresistive sensor to be calibrated to an accuracy of 0,5 %FS over a potential temperature range of 100 K.
A temperature sensor divides the temperature range into fields with a width of 1,5 K each. Two values are assigned to each field in an EEPROM: one value for the zero point and another for the amplification, determined by mathematical interpolation in the calibration process. During operation, the corresponding values are ‚switched in’ at the relevant temperatures. The electronics make it possible to assign up to 120 fields so that a temperature range of 180 K can be covered. The 100 K restriction for series 21 PY is due to the sensor
This means that more or less any temperature can be the ‚calibration temperature’ for these transmitters. Calibration and temperature errors within a temperature field are within ± 0,2 %FS. The remainder of the error bandwidth of ± 0,5 %FS can be attributed to linearity and stability errors. So it’s goodbye to the days when sensor engineers had to struggle every day with TKN (zero point) and TKG (gain/amplification) problems.
The 21 PY product line is outstanding due to its extreme ruggedness towards electromagnetic fields. The limits of the CE standard are undercut by a factor of up to 10 with conducted and radiated fields, thus making this product ideal for use in harsh industrial environments.
The Y-line transmitters have an extremely small temperature error. This is achieved using an additional circuit containing a temperature sensor that subdivides the temperature range into fields that are 1,5 Kelvin (K) wide. The TK zero and TK compensation values are calculated for each field and programmed into the additional circuit. During operation, these values are fed into the analogue signal path depending on the temperature. Each temperature is the "calibration temperature" for this transmitter.
The Series 23 (S)Y/25 Y product line is outstanding due to its extreme ruggedness towards electromagnetic fields. The limits of the CE standard are undercut by a factor of up to 10 with conducted and radiated fields.
LEO 2 is a compact, micro-processor (µP) controlled, highly accurate and versatile pressure measuring instrument with digital indication. The piezoresistive pressure transducer as the heart of the instrument has gone through extensive pressure- and temperature tests. Its characteristics are stored in the instruments internal EEPROM. The µP of the LEO 2 reads the characteristic values and calculates therefrom the pressure to an accuracy of < 0,1 %FS at room temperature.
The pressure is measured twice per second and displayed. The top display indicates the actual pressure, the bottom display shows the Max.- or Min.- pressure since the last RESET.
Also available as intrinsically safe version (LEO 2 Ei).
The LEO 5 combines the notable features of Keller’s successful LEO-Record and LEX 1 digital pressure gauges, featuring an IP66-rated stainless steel enclosure. This robust housing combines contemporary microcontroller-based electronics and capacitive-touch controls, operated through the environmentally-sealed safety glass front panel. The large backlit LCD display ensures readability in any lighting conditions.
Two selectable measurement modes, standard and peak, are included to ensure maximum versatility. In standard mode, high-resolution pressure measurements are taken twice per second. When operating in peak mode, sampling frequency increases to 5 kHz with 16 bit resolution.
The LEO 5 interfaces with a PC via USB connectivity, allowing access to active measurements and recorded data including pressure, peak pressure, temperature, and measurement interval. PC connection also allows device configuration, firmware updates, and recharging of the integral accumulator power supply.
The unique modular design of the LEO 5 makes possible adaptation to customer-specific measuring requirements.
LEO 5 CA offers a user-friendly way to represent the pressure measurement at the bottom of a tank as the quantity of remaining liquid. At the push of a button, the microcontroller performs the calculations using the information of the tank shape and dimensions and displays the remaining tank content quantity on the clearly legible 5-digit LED display in the desired unit (litres, gallons etc.).
The unit is configured using a PC and the easy-to-use software so that the filling level, which determines the pressure, can be converted into an appropriate filling quantity. First the tank shape is selected, then the tank dimensions and the specific gravity of the liquid are entered. It contains the most current tank shapes. The program covers the most common tank shapes, but also enables any shape by entering the parameters into a specified table.
The exclusive use of absolute pressure sensors in the LEO 5 CA system eliminates the use of capillary vented cables with all the problems associated with a gauge pressure measurement. The LEO 5 CA housing integrates an air pressure sensor, ranged between 0,8 bar and 1,2 bar absolute. The sensors to measure the hydrostatic pressure at the bottom of the tank are calibrated from 0,8 to 1,8 bar abs for tanks up to 5 m in height, and 0,8 to 2,3 bar abs for tanks up to 10 m in height. The pressure difference, calculated by the micro-controller, is the relative hydrostatic pressure. The content of a pressurised tank is determined using the difference between the measurements from two absolute pressure sensors located at the top and bottom of the tank
An accuracy of the system of up to 2 mbar (corresponding to a 2 cm water column) is achieved using a computerised calibration and compensation procedure for the pressure sensors.
LEO 5 CA makes it possible to connect various pressure probe transmitter versions (with thread, front-flush with flange, or submersible sensors).
The power supply to the system (8 to 28 V) can be provided externally or internally from an accumulator or a battery. The display is obtained by pressing the button on the front, and the value appears for a configurable duration. The LEO 5 CA has two switch outputs with configurable functionality and threshold values. The device must be supplied externally if the switch outputs are used.
LEO Record is an autonomous battery powered instrument with digital display designed to record pressure and temperature over long periods.
The pressure is measured and displayed once per second (shortest interval). The top display indicates the actual pressure, the bottom display shows the record status. All LEO Record versions have two operating keys. The left key is to turn the instrument on, to select the functions and the pressure units. The right key executes the selected function or unit.:
The remote data transmission unit ARC1-Tube with logger function is encased in a robust, stainless steel housing, which is ideally suited to installation in 2" monitoring pipes. This unit records measurements made by external sensors (e.g. a level sensor) and periodically transmits the collected data via 2G, 3G, 4G, NB-IoT, LTE-M or LoRaWAN. The high-performance battery and sophisticated power management enable autonomous operation for up to 10 years. KELLER provides a range of licence-free software solutions for configuration and data processing. The easiest and most convenient way to access the collected data is via KOLIBRI Cloud.
The remote data transmission unit ARC1-Box with logger function is encased in a robust, water-tight aluminium housing. This unit records measurements made by external sensors (e.g. a level sensor) and periodically transmits the collected data via 2G, 3G, 4G or LoRaWAN. The high-performance battery and sophisticated power management enable autonomous operation for up to 10 years. KELLER provides a range of licence-free software solutions for configuration and data processing. The easiest and most convenient way to access the collected data is via KOLIBRI Cloud.
The remote data transmission unit ARC1-Box-SB with logger function is equipped with safety barriers and, in combination with intrinsically safe transmitters, it is suitable for use in hazardous applications. The unit is encased in a robust, water-tight aluminium housing. It records measurements made by external sensors (e.g. a level sensor) and periodically transmits the collected data via 2G, 3G, 4G or LoRaWAN. The high-performance battery and sophisticated power management enable autonomous operation for up to 10 years. KELLER provides a range of licence-free software solutions for configuration and data processing. The easiest and most convenient way to access the collected data is via KOLIBRI Cloud.
The remote data transmission unit ADT1-Tube is encased in a robust, stainless steel housing, which is ideally suited to installation in 2" monitoring pipes. The LoRa module, which can be configured on a country-specific basis, establishes a connection with the Internet and makes it possible to collect measurement data in a low-cost and energy-saving manner. These autonomous devices can be linked with digital level sensors and pressure transmitters in the KELLER D and X product lines. With three conventional, high-quality AA batteries, the system can operate autonomously for up to 5 years. The LoRaWAN provider can be selected freely or an in-house or open source infrastructure and associated services can be used. The easiest and most convenient way to access the collected data at the end of the transmission chain is via KOLIBRI Cloud from KELLER.