Low pressure signals need stable measurement, especially in ventilation, filter monitoring and clean room control. HD404 transmitters measure relative pressure to atmosphere or differential pressure, with analog versions covering 50…1000 Pa and RS485 Modbus-RTU versions available for 250 Pa, 1000 Pa or 100 mbar ranges.
The temperature-compensated piezoresistive sensor supports excellent linearity, repeatability and stability over time. For applications where zero drift matters, AZ versions periodically equalize the differential pressure at the sensor input, compensate offset and remain insensitive to mounting position.
System integration is straightforward in HVAC and building automation installations. Outputs include 0…10 V, active 4…20 mA or RS485 Modbus-RTU, with optional 4-digit LCD for local reading. SR versions convert pressure into airflow speed for Pitot or Darcy tube applications and can also display calculated airflow speed when combined with the LCD option.
The series measures relative pressure to atmosphere or differential pressure. Analog models use G versions for 0…+f.s. relative pressure and D versions for -f.s.…+f.s. differential pressure.
Analog models allow selection between LOW and HIGH measuring ranges by dip switch, helping match the output scale to the application.
Versions with option L include a 4-digit LCD that shows pressure in the selected measurement unit. SR versions with display can also show calculated airflow speed.
FAST mode provides 0.125 s response in pressure mode. SLOW mode can be configured to 1, 2 or 4 s, and is recommended where airflow turbulence is present.
HD404ST models support configurable Modbus address, baud rate and communication parameters, with built-in RS485 line termination selectable by jumper.
The wall-mounted ABS housing includes Ø 6 mm pressure connections, nickel-plated brass fittings, screw terminals and a PG9 cable gland.
Code: HD404T [1] [2] [3] [4] [5]
Example: HD404T3PGAZSR
[1] Nominal Full Scale (f.s.)
1P = 100 Pa
1M = 10 mmH2O
1I = 0,4” H2O
2P = 250 Pa
2M = 25 mmH2O
2I = 0,8” H2O
3P = 500 Pa
3M = 50 mmH2O
3I = 2” H2O
4P = 1000 Pa
4M = 100 mmH2O
4I = 4” H2O
[2] Measurement type
D = differential pressure –f.s.…+f.s
G = relative pressure with respect to the atmosphere 0…+f.s.
[3] Autozero option
Blank = without autozero (not possible for HD404T1 – HD404T2)
AZ = with autozero circuit (mandatory for HD404T1 – HD404T2)
[4] Display
Blank = without display
L = with LCD display
[5] Output type
Blank = pressure output
SR = air speed output (only G versions)
Code: HD404ST [1] [2] [3] [4]
Example: HD404ST2AZLSR
[1] Nominal Full Scale (f.s.)
2 = -250 … +250 Pa
4 = -1000 … +1000 Pa
5 = -100 … +100 mbar
[2] Autozero option
Blank = without autozero (not possible for HD404ST2)
AZ = with autozero circuit (mandatory for HD404ST2)
[3] Display
Blank = without display
L = with LCD display
[4] Output type
Blank = pressure output
SR = air speed output (only G versions)
