Hydac HDA 4445-A-400-000 Pressure Transmitter, 400 bar

Rugged 400 bar sensing for mobile and industrial hydraulics

The Hydac HDA 4445-A-400-000 (HYDAC part number 906209) belongs to the HDA 4400 series, which uses a stainless steel membrane with a thin-film strain gauge as the pressure cell. The output is a two-wire 4 to 20 mA loop, and this code is built for a 400 bar range, a G1/4 A male port and the DIN-style EN175301-803 plug with its mating connector.

HDA 4400 transmitters are the more economical sibling of the HDA 4700 line: the headline accuracy is 0.5 % FS rather than 0.25 %, but the shock rating of 100 g is high and the 1 ms rise time suits fast pump and valve circuits.

Technical specifications

Model code and options

The pattern is HDA 4 4 X X – X – XXXX – 000. Here the fourth digit 4 means G1/4 A male, the fifth digit 5 is the three-pole plus PE plug, A is 4 to 20 mA and 400 is the range in bar. Changing the fifth digit to 6 gives a four-pole M12x1 connector, which the datasheet lists as IP 67 when a suitable connector is fitted but supplied without the mating part. The datasheet also lists output B (0 to 10 V, three conductors).

Choosing between HDA 4400 and HDA 4700

Where the application needs better than 0.5 % accuracy, or a 0.25 % best fit figure, look at the HDA 4700 series. For plain monitoring of pump pressure, clamping pressure and accumulator charge, the HDA 4400 usually has enough precision. Check that the fluid is compatible with FKM seals, and confirm the thread and plug before ordering. This page cites the HYDAC USA datasheet, which prints psi and SAE-6 codes; the bar and G1/4 code above follows the same structure.

Mount the transmitter with the port facing down or sideways where possible so that air does not collect in front of the membrane, and use the recommended 20 N·m torque with a matching sealing ring. Run the signal cable away from motor leads, because the 4 to 20 mA loop is robust but not immune to heavy switching noise. In oil circuits with strong pressure peaks, a damping orifice or snubber ahead of the sensor extends service life.

Is the 400 bar range the right choice?

Choose the measuring range from the highest normal working pressure of the circuit, not from the relief valve setting alone, and then check that pressure spikes stay below the overload rating. A range that is much larger than the working pressure wastes resolution, because accuracy is stated as a percentage of full scale; a circuit that normally runs at a fraction of 400 bar may be better served by a lower range from the same series. On the other hand, circuits with hammer from fast-closing valves or cylinders hitting end stops benefit from the headroom between the measuring range and the overload and burst figures.

• Confirm the port in the manifold or test point matches the G1/4 A male thread, and order an adapter if it does not.
• Check the hydraulic fluid against the FKM seal, especially with water-glycol or phosphate ester fluids.
• Decide early whether the DIN plug or the M12 connector suits the machine wiring standard.

Wiring and loop check

As a two-wire device, the transmitter takes its power from the 4 to 20 mA loop, so the supply voltage at the sensor terminals must stay above the minimum after the voltage drop across the PLC input and long cables. Use the load resistance formula in the specification table to check this before installation. At commissioning, with the system depressurised, the loop should read close to 4 mA; raise the pressure in steps against a reference gauge and compare the readings with the PLC scaling. Recording these values at handover gives a baseline for later checks.

Maintenance and troubleshooting

A reading stuck at or below 4 mA usually points to a wiring fault, a missing supply or a reversed loop, while a reading pinned above 20 mA indicates over-range pressure or a damaged sensor. An unstable or noisy signal often comes from a poor screen connection or a cable running beside motor leads. If the reading drifts gradually, compare it with a calibrated gauge before replacing the transmitter, keeping in mind the long-term drift figure quoted in the specifications. When removing the sensor, always release system pressure first and replace the sealing ring when refitting.

Application notes for Oman and GCC conditions

Mobile hydraulics, cranes, drilling rigs and press lines in Oman see high ambient heat, and hydraulic oil temperatures rise with it; keep the fluid within the permitted temperature range, and position the transmitter away from hot exhaust or radiator outflow. Sand and dust work into connectors, so make sure the DIN plug gasket is fitted and the screw tightened to maintain the IP rating, or choose the M12 version with a sealed cordset for outdoor machines. On coastal sites and offshore-related equipment, salt spray can attack connector pins and cable glands; use protective caps on spare connectors, apply suitable contact protection, and route cables so that water drains away from the plug rather than into it.

Documents and quotation

The datasheet for the HDA 4400 series is attached. Please quote the full model code and quantity. See also our pressure instrumentation range.