Hydac HDA 4745-A-400-000 Pressure Transmitter, 400 bar

A compact 400 bar transmitter for hydraulic pressure lines

The Hydac HDA 4745-A-400-000 (HYDAC part number 906393) is a two-wire pressure transmitter from the HDA 4700 series. A thin-film strain gauge on a stainless steel membrane converts the line pressure into a 4 to 20 mA signal, so it connects to a PLC analogue input or a HYDAC display without extra signal conditioning. This particular code covers the 0 to 400 bar range, G1/4 A male thread and the EN175301-803 plug connector.

The series is aimed at mobile and industrial hydraulics and pneumatics where space is tight. Typical points of use are pump outlets, accumulator circuits, press and clamping lines and test points on power units.

Technical specifications

Reading the model code

The code follows the pattern HDA 4 7 X X – X – XXX – 000. In 4745-A-400-000 the fourth digit 4 selects the G1/4 A male connection, the fifth digit 5 selects the EN175301-803 plug (3 pole + PE), the letter A selects 4 to 20 mA and 400 is the range in bar. The trailing 000 is the standard modification number. A 6 in the fifth position would give an M12x1 four-pole plug without mating connector, and a B in the signal position gives 0 to 10 V on three conductors.

Selection and wiring notes

Choose a range with some headroom over the highest working pressure, because pressure peaks above the measuring range are limited only by the 800 bar overload rating. On the EN175301-803 plug, pin 1 carries signal plus, pin 2 signal minus and pin 3 is not connected, with the housing as earth. Reverse-polarity, over-voltage and short-circuit protection are built in. The part number sits in a family that also includes 60, 100, 250 and 600 bar versions, so confirm range, thread and plug before ordering. The datasheet linked here is the HYDAC USA edition, which prints psi and SAE-6 codes; the bar and G1/4 versions follow the same code structure.

For installation, tighten the G1/4 A thread to 20 N·m with a suitable sealing ring and fit the plug so that the cable gland points downward, which keeps water out of the connector. A damping orifice is recommended on lines with fast pressure peaks.

Key features of the HDA 4745-A-400-000

• Thin-film strain gauge cell – the measuring element is deposited directly on a stainless steel diaphragm, giving good long-term stability and resistance to pressure peaks.
• Two-wire current loop – the 4 to 20 mA signal is robust against electrical noise and cable resistance, and a reading below 4 mA makes a broken wire easy to detect.
• High overload and burst margins – the specified overload and burst pressures give a safety reserve against pressure spikes common in hydraulic systems.
• Fast response – short rise time allows pressure peaks and switching events to be captured by the control system.
• Vibration resistant – suitable for mounting directly on power units, mobile machines and pump blocks.
• Standard connections – G1/4 A thread and the EN175301-803 plug are widely used, so replacement is straightforward.

Typical applications

• Pump outlet and system pressure monitoring on hydraulic power units.
• Accumulator pre-charge and charging pressure supervision.
• Press, clamping and injection moulding machine control.
• Mobile hydraulics on cranes, construction and mining equipment.
• Test benches and condition monitoring of hydraulic circuits.

Installation and maintenance tips

• Install the transmitter where it can be isolated and vented, for example through a test point adapter or a gauge isolator valve, so it can be replaced without draining the system.
• Seal the G1/4 A thread with the profile seal on the transmitter, not with tape or paste, and tighten to the specified torque.
• Where severe pressure spikes or cavitation occur near pumps or valves, consider a snubber or a mounting point further from the source.
• Fit the supplied mating connector correctly with its gasket to maintain the IP rating, and route the cable with strain relief.
• Ground the cable shield according to the plant’s EMC concept and keep the signal cable away from solenoid and motor cables.
• Check zero output at atmospheric pressure during scheduled maintenance as a quick plausibility check.

Wiring the current loop

In a two-wire loop, the transmitter, the supply and the input of the PLC or display are connected in series. The available supply voltage minus the minimum voltage the transmitter needs, divided by the maximum loop current, gives the maximum allowable loop resistance – the formula in the specification table expresses this. Include the input resistance of the PLC card and the resistance of long cable runs in the calculation, particularly on mobile machines where supply voltage can fall during engine cranking.

Use in Oman and GCC conditions

Hydraulic systems in Oman’s oil and gas fields, ports, steel and aluminium plants and construction fleets often run in high ambient temperatures and dusty air. The transmitter’s operating and fluid temperature ranges should be checked against the actual oil temperature at the mounting point, which can be considerably higher than ambient on heavily loaded power units. Keeping the connector sealed and protected from direct jets during wash-down, and shading exposed transmitters on outdoor equipment, help long service life. FKM seals suit common mineral hydraulic oils; for special fluids, confirm seal compatibility with HYDAC.

What to include in your RFQ

Give the full model code HDA 4745-A-400-000 and part number 906393, the quantity and whether you need extra mating connectors, cables, test point adapters or a HYDAC display. For replacements, include the label details of the installed transmitter so the range, signal and connector can be confirmed.

Documents and quotation

The manufacturer datasheet for the HDA 4700 series is attached. Send the full model code, quantity and delivery location with your enquiry. Related reading: our pressure instrumentation range.