KELLER Series 41X Capacitive Low-Pressure Transmitter 30 mbar

KELLER Series 41X is a capacitive pressure transmitter for very low pressures: full-scale ranges of 30, 100 and 300 mbar, with resolution of 1 microbar. It combines a ceramic measurement cell with the microprocessor electronics of KELLER digital Series 30, so it offers both an analog output and an RS485 interface.

Micro-pressure measurement with polynomial compensation

KELLER states that the 41X pressure value is derived from the pressure and temperature sensor signals by a polynomial P(S,T) = A(T).S0 + B(T).S1 + C(T).S2 + D(T).S3, whose coefficients are measured at several pressure and temperature points at the factory and stored in the EEPROM. The compensated range is 10…50 degC and the error band is at most 0.2 %FS.

The transmitter is calibrated to its base range, and the CCS30 software can re-scale the analog output to any section within it, for example 4…20 mA over 20…60 mbar on a 100 mbar range. Up to 128 transmitters can share one bus.

Key features as printed in the datasheet

• Ranges 30, 100 and 300 mbar (PR-41X relative, PD-41X differential); 1 mbar full range by splitting the 30 mbar range.
• Error band max. 0.2 %FS; stability 0.1 %FS (100 mbar and above) or 0.1 mbar.
• 2-wire 4…20 mA (8…28 VDC) or 3-wire 0…10 V (13…28 VDC).
• RS485 half-duplex, Modbus RTU and KELLER bus; up to 128 devices on one bus.
• Intrinsically safe 41X-Ei version, 10…30 VDC supply.

Technical specification

Performance and electrical data

Mechanical data

Selection and ordering guide

Choose the full-scale range closest above your maximum pressure: the error band is proportional, so scaling a 300 mbar transmitter down to a small span raises the error accordingly, as the datasheet warns. For higher ranges or wet-wet differential service, KELLER points to Series 33X and 39X.

Options include negative or bidirectional ranges such as -10…+10 mbar, alternative plugs, a cable version, and the intrinsically safe 41X-Ei, which may only be used with certified intrinsically safe equipment.

Installation and operation notes

The overpressure ratings are low (300 mbar on the 30 mbar range), so pressurise slowly and avoid pressure surges when connecting. The PD-41X reference side is limited to non-aggressive dry gases.

Zero point and amplification can be re-adjusted through the CCS30 software, and the low-pass filter, address and baud rate are configurable. KELLER recommends its K-114 RS485-USB converter for reliable communication.

Applications in Oman and the GCC

Low-range transmitters monitor duct and room differential pressure, cleanroom and fume-cupboard pressure, burner draught, filter condition and tank blanketing. These matter in HVAC and process areas of GCC plants, wherever small air-side pressure drops must be read accurately. Because the housing is IP40 and 50 mm in diameter, mount it inside a cabinet or enclosure rather than outdoors, and keep the pressure tube short and sloping so that no condensate collects in the line.

Compatible accessories and related items

KELLER lists the 33X for higher ranges and Series 39X for wet-wet differential duty. The 33X and PD-33X are also listed on this site. Confirm the base range, output type, connector and whether the intrinsically safe Ei version is needed before ordering.

Related KELLER products: KELLER Series 21Y Compact Pressure Transmitter 4-20 mA, KELLER Series 23SY Pressure Transmitter 0.1 to 1000 bar, KELLER Series PD-33X Differential Pressure Transmitter, KELLER Series 33X High-Accuracy Pressure Transmitter RS485, KELLER Series 35X Front-Flush Pressure Transmitter RS485 and KELLER Series 21C Ratiometric 0.5-4.5 V Pressure Transmitter.

Documents and quotation

For quotation, send your required quantity and destination. The KELLER datasheet for 41X is provided below the description on this page. Seven Star LLC works as an independent supplier from Muscat. Please compare code, ratings and approvals with the document before you place an order; see also the category listing.