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Keller Series PD-39X

sku Product SKU:  KEL-39Xs

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.

Digital Interface

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.

Analog Output

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).

ZAR 0,0000


Keller LEO5-BT

sku Product SKU:  KEL-LEO5-BT

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.

ZAR 0,0000



sku Product SKU:  LTR-LPP08

The pressure test pump LR-Cal LPP 08 is used to generate pressure and vacuum for checking, adjusting and calibrating mechanical and electronic pressure measuring instruments by comparative measurements in the low-pressure and vacuum range. The pressure tests may be carried out in laboratories, workshops or on-site at the measuring point.

If the instrument to be tested and a sufficiently accurate reference measuring instrument are connected up to the pressure test pump, the same pressure is applied to the two measuring instruments when the pump is operated. By comparing the two measure values at random pressure values, the accuracy can be verified or the unit under test can be adjusted.

The LR-Cal LPP 08 is a pneumatic pressure test pump for low-pressure ranges up to 8 bar with a change-over switch to vacuum down to -850 mbar. Despite its compact dimensions, the pressure test pump is easy to operate and allows for the exact generation of the required test pressures. The maximum pressure or vacuum achievable depends on the attached test volume. The smooth-running pressure generation and the integrated fine adjustment valve allow a safe and precise setting of very small positive resp. negative pressure values in the range of mbar.

The unit under test and the reference instrument can be easily connected with the supplied accessories.

Included in the scope of standard delivery:

  • Pressure test pump LR-Cal LPP 08
  • T-piece, one side with 1/8" BSP male thread for direct mounting to the pressure test pump, other sides with quick hose connectors (Push&Pull) for pneumatic hose 4 x 2 mm. Easy mounting thanks to supplied o-ring. Max. torque 15 Nm.
  • 2 pcs. pneumatic hose 4 x 2 mm, each length 0.5 m
  • 2 pcs. quick connectors (Push&Pull) with 1/8" BSP male thread, for hose 4 x 2 mm
  • 1 Adapter 1/8" BSP female x 1/2" BSP female, for connecting reference instrument (with 1/2" BSP male thread)
    Thanks to integrated o-ring tightening without tools, just by hand
  • 1 Adapter 1/8" BSP female x 1/4" BSP female, for connecting unit under test (with 1/4" BSP male thread)
    Thanks to integrated o-ring tightening without tools, just by hand
  • Operating manual

ZAR 0,0000



sku Product SKU:  LTR-LDW-P

Proven primary
pressure standard
Deadweight Tester / Pressure Balances are the most accurate instrument available on the market for the calibration of electronic or mechanical pressure measuring instruments. The direct measurement of the pressure (p = F / A), as well as the use of high-quality materials enable a very small measurement uncertainty, in conjunction with an excellent long-term stability of 5 years (recommended in accordance with German Calibration Service DAkkS).
The deadweight tester / pressure balance has therefore been used for years in factory and calibration laboratories in national institutes, research laboratories and in industry.

Stand-alone operation
Due to its integrated pressure generation and the pure mechanical measuring principle, the model LR-Cal LDW-P is ideal for on-site use for maintenance and service.

Basic principle
Pressure is defined as the quotient of force and area. The core component of the model LR-Cal LDW-P is therefore a very pecisely manufatured piston-cylinder-system, which is loaded with masses in order to generate the individual test points.
The masses applied are proportional to the target pressure and this is achieved through optimally graduated weights. As standard, these masses are manufactured to the standard gravity (9.80665 m/s²), though the can be manufactured to a specific location (gravity) and also DAkkS-calibrated.

Easy operation
Depending on the instrument version the pressure is set via an integrated pump or via an external pressure supply by the use of control valves. For fine adjustment a very precisely adjustable spindle pump with a precision spindle running only within the pump body is mounted.
As soon as the measuring system reaches equilibrium, there is a balance of forces between the pressure and the mass load applied. The excellent quality of the system ensures that this pressure remains stable over several minutes, so that the pressure value for comparative measurements can be read without any problems, or also so that more complex adjustments can be carried out on the item under test.

ZAR 0,0000


Keller Series 21Y

sku Product SKU:  KEL-21Ys

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.

ZAR 0,0000


Keller Series 21PY

sku Product SKU:  KEL-21PYs

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.

ZAR 0,0000


Keller Series 33X

sku Product SKU:  KEL-33Xs

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.

ZAR 0,0000


Keller Series PRD-33X

sku Product SKU:  KEL-PRD-33Xs

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.

ZAR 0,0000

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