Senseca

HD404 Low Pressure Transmitter

Relative and differential low pressure transmitters for clean room, filter, flow and HVAC applications.

Measures from 50 to 1000 Pa on analog models and 250 Pa, 1000 Pa or 100 mbar on RS485 Modbus-RTU models
Outputs of 0…10 V, 4…20 mA active or RS485 Modbus-RTU
Optional auto-zero (AZ), 4-digit LCD (L) and square-root airflow speed version (SR)

Quantity

Overview

The HD404… series consists of low pressure transmitters for relative pressure (to atmosphere) or differential pressure measurement. Depending on the version, it covers 50…1000 Pa for analog models and 250 Pa / 1000 Pa / 100 mbar for RS485 Modbus-RTU models. The sensor signal is converted into 0…10 V, 4…20 mA active, or RS485 Modbus-RTU output, ensuring reliable transmission also over long distances with high noise immunity.

Typical applications

Clean room monitoring
Filter control
Flow measurement
Air conditioning control
Ventilation control

Key Features

Micromachined, temperature-compensated silicon sensor, designed for excellent linearity, repeatability and long-term stability
Auto-zero versions (AZ) for long-term stability: periodic offset correction compensates zero drift and sensor aging, reducing maintenance, and AZ versions are also insensitive to mounting position
Direct local indication with the optional 4-digit LCD (L) in the selected measurement unit, useful for commissioning and on-site checks
Square-root version for airflow applications (SR), optimised for Pitot/Darcy tubes with output proportional to airflow speed. With the display option it can show both measured pressure and calculated airflow speed
Robust signal conditioning for industrial environments, with high noise immunity for HVAC and building automation installations
Analog models: range selection via dip switch between two measurement ranges
SR models: set the Pitot/Darcy tube coefficient and calculation parameters (air temperature, barometric pressure, duct static differential pressure). On analog versions, the full-scale speed for the output can be set
Factory calibrated and supplied ready for installation and commissioning

Benefits

Accurate even at very low pressure: stable measurements down to 50 Pa
Outputs for easy integration: 0…10 V, 4…20 mA active or RS485 Modbus-RTU
Display option for direct reading: 4-digit LCD with selectable engineering units
Auto-zero for low maintenance: offset correction and drift compensation over time (AZ versions)
Airflow speed option (SR): square-root output for Pitot/Darcy applications, with airflow display on L versions

Specifications

MEASUREMENT SPECIFICATIONS
Sensor	Piezoresistive
Measuring range	From 50 to 1000 Pa (from 0.2" H2O to 4" H2O) for the versions with analog output; 250 Pa / 1000 Pa / 100 mbar for the versions with RS485 Modbus RTU output
Accuracy*	±(0.8% measure + 0.5) Pa with AZ option
Long-term stability*	<±0.2 Pa with AZ option
Resolution	HD404TxP…: 0.5 Pa (f.s. ≤ 500 Pa) / 1 Pa HD404TxM…: 0.05 mmH2O (f.s. ≤ 50 mmH2O) / 0.1 mmH2O HD404TxI…: 0.002" H2O HD404ST2…: 0.1 Pa HD404ST4…: 1 Pa HD404ST5…: 0.1 mbar HD404…SR: 0.01 m/s
Overpressure limit	50 kPa
*	Refer to the manual for non-AZ versions and other units of measurement

TECHNICAL SPECIFICATIONS
Output	0…10 Vdc or active 4…20 mA (HD404T…) RS485 Modbus-RTU (HD404ST…)
Power supply	24 Vac ± 10% or 18…40 Vdc (HD404T…) 12…30 Vdc (HD404ST…)
Absorption	< 1 W @ 24 Vdc (HD404T…) < 100 mW @ 12 Vdc (HD404ST…)
Electrical connections	Screw terminal block, max 1.5 mm2, PG9 cable gland
Connection to PC	Modbus model: RS485 serial port. Connection to a USB port by using RS485 adapter. All other models: RS232 serial port. Connection to a USB port by using CP27 cable.
Response time	HD404T… with dip-switch set to FAST: 0.125 s in pressure mode; 1 s in speed mode (only SR versions) HD404T… with dip-switch set to LOW: configurable 1, 2 or 4 s (default 2 s) HD404ST…: configurable 0.125, 1, 2 or 4 s (default 2 s)
Zero calibration	Automatic for the versions with AZ option

PHYSICAL SPECIFICATIONS
Pressure connections	Ø 6 mm
Compatible media	Only air and non-aggressive dry gases
Operating conditions	-10…+60 °C (-5…+50 °C for the models with AZ option), 0…95 %RH
Storage temperature	-20…+70 °C
Materials	Housing: ABS Pressure connections: nickel-plated brass
Protection degree	IP65
Supplied with	2 m of silicone tubing Ø5 mm internal / Ø8 mm external and two plastic fittings for ducts. PC connecting cable must be ordered separately.