KELLER Series 33X High-Accuracy Pressure Transmitter RS485

KELLER Series 33X is a piezoresistive pressure transmitter with accuracy down to 0.01 %FS and a digital RS485 interface (Modbus RTU) that can run alongside a 4…20 mA or voltage output. It covers 0…0.3 to 0…1000 bar and is aimed at laboratory use, test benches, gauge standards and precision industrial measurement.

Digital precision with a rangeable analog output

The 33X is an X-line product: the sensor is an insulated, encapsulated piezoresistive chip with mathematical compensation, and values are read digitally with a resolution of 0.0005 %FS at an internal rate of 1800 Hz or more. The analog interface can be re-ranged (turn-down) through the digital interface, smallest span 0.1 bar, with no surcharge on the standard ranges.

Standard accuracy is 0.05 %FS with a KELLER test report; the optional increased precision of 0.01 or 0.025 %FS applies to absolute (PAA/PA) versions of 10 bar and above on the RS485 interface, and can be backed by an accredited DAkkS calibration certificate.

Key features as printed in the datasheet

• Accuracy 0.05 %FS; optional 0.01 %FS precision (digital, PAA/PA, 10 bar and above).
• Total error band 0.05 %FS at 10…40 degC and 0.1 %FS at -10…80 degC.
• RS485 half-duplex, Modbus RTU and KELLER bus; up to 1.2 km lines; 9600 or 115,200 bit/s.
• Long-term stability typ. 0.05 %FS, max. 0.1 %FS per year.
• Ten-million-cycle endurance below 600 bar.

Technical specification

Performance and electrical data

Mechanical and environmental data

Selection and ordering guide

The standard range table runs 0…0.3, 1, 3, 6, 10, 16, 30, 60, 100, 300, 700 and 1000 bar, with proof pressures from 3 bar up to 1100 bar. PAA is referenced to vacuum, PA to 1 bar abs and PR to atmosphere; intermediate and negative ranges are possible for the analog output.

Select the compensated temperature range (10…40 degC or -10…80 degC) as an ordering option, and decide early whether you need the increased-precision or DAkkS-certified version, since it is limited to PAA/PA, 10 bar and above, and excludes 4…20 mA.

Installation and operation notes

Configure addresses, baud rates and analog scaling with the licence-free CCS30 software over an RS485-USB converter; KELLER recommends its K-114 converter. During communication the 4…20 mA signal of 2-wire types is disturbed, whereas 3-wire types can run analog and digital together.

For pressures at or below 0.1 bar abs KELLER recommends a vacuum-optimised version, and for ultra-dynamic applications the fully welded 23SX series. The device is calibrated with the connection facing down.

Applications in Oman and the GCC

A 0.01 to 0.05 %FS transmitter suits calibration benches, pressure standards, flow-test rigs and R&D in Gulf universities and laboratories, as well as precision monitoring on process skids. Digital readout over Modbus integrates with PLCs and data loggers without analog drift.

Compatible accessories and related items

KELLER names PD-33X (differential), 33Xc (CANopen), 35X (front-flush) and 23SX (fully welded) as similar products; the PD-33X and 35X are also listed on this site.

Frequently asked questions

What accuracy does the 33X reach?

0.05 %FS as standard and 0.01 %FS with the optional increased precision on digital output.

Which digital protocols are supported?

Modbus RTU and the KELLER bus over RS485 half-duplex.

Can analog and digital outputs run together?

3-wire types can; on 2-wire 4…20 mA types the loop is disturbed during communication.

What pressure connections are listed?

G1/4, G1/2, NPT, M20x1.5, Mano and UNF/JIC variants as shown in the datasheet.

Does Seven Star LLC act as a KELLER distributor?

No. Seven Star LLC is not a KELLER distributor; it is an independent Muscat-based supplier that quotes KELLER products on request.

Documents and quotation

The official KELLER datasheet for 33X is hosted on this page for download. Seven Star LLC is an independent supplier in Muscat; send your quantity and delivery location through the quotation form and we will quote this item. Please confirm the exact order code, ratings and approvals against the document before ordering. More related products: product category.