Sensors for HVAC & Building Services
Low-range differential pressure, temperature and flow measurement for air handling units, chilled water loops and cleanroom cascades, where small signals and long cable runs are the norm.
HVAC measurement is a low-signal discipline. A filter differential pressure of 120 Pa on a 0-1,000 Pa transmitter uses 12% of the range, and the same transmitter asked to hold a cleanroom cascade needs a resolution the device was never designed for. Selecting the range to the application, rather than to the worst case, is the single biggest improvement available in most buildings.
Our HVAC range covers differential pressure transmitters from 0-50 Pa to 0-10 kPa, duct and immersion temperature sensors with matched transmitters, chilled and hot water flow meters, and humidity sensors for AHUs. Outputs are 4-20 mA, 0-10 V, Modbus RTU and BACnet MS/TP on selected models.
For energy metering we supply matched temperature pairs and flow meters, because a billing-grade heat meter is only as good as the temperature difference measurement. A 0.1 °C error on a 10 °C delta is a 1% error on the energy total, every hour of every day.
Application Reality
What actually goes wrong here
These are the failure modes we are called in to solve, and the specification change that addresses each one.
Small signals on a wide range
A 0-1,000 Pa transmitter measuring a 120 Pa filter drop wastes most of its resolution. A 0-250 Pa unit gives four times the resolution for the same cost.
Impulse line errors
Unequal tubing length or a trapped water slug creates an offset that looks like a real reading. Equal-length, short, downward-sloping impulse lines remove most of it.
Long analogue runs
0-10 V signals degrade over long cable runs; 4-20 mA does not. In a plant room, current loop or Modbus is always the better choice.
Energy metering accuracy
Heat metering depends on the temperature difference. Matched pairs, installed at the correct immersion depth, are what makes a meter defensible.
Condensate in ducts
A duct-mounted sensor in a humid airstream collects water. Mounting orientation and a drain leg matter as much as the IP rating.
Products
Specified for hvac systems applications
DM-FV40-VX-025
DM-FV40 Vortex Flow Meter for Steam and Gas, DN15-DN300
DM-FE150-CL-600
DM-FE150 Clamp-On Ultrasonic Flow Meter, DN15-DN600
DM-TS100-PT100-4W
DM-TS100 PT100 RTD Probe, -50 to +400 °C
DM-PD100-DP-10K
DM-PD100 Differential Pressure Transmitter, 0-10 kPa
DM-PS500-SPDT-10
DM-PS500 Compact Pressure Switch, 0.5-10 bar
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Standards
What the audit will ask for
| Standard | Requirement |
|---|---|
| EN 60529 IP54/IP65 | Dust and water protection for plant rooms |
| BACnet / Modbus | BMS integration protocol |
| EN 1434 (heat meters) | Energy metering accuracy class |
| ASHRAE 62.1 ventilation | Outdoor air measurement for DCV |
Application Example
Cleanroom cascade stability, electronics plant
Situation
An electronics manufacturer was chasing differential pressure alarms in a class 10,000 area, with the BMS logging swings of 15 Pa on a 20 Pa setpoint.
What we changed
The 0-1,000 Pa transmitters were replaced with 0-100 Pa units, mounted within 2 m of the room tap with equal-length impulse lines and a dedicated 24 V supply, and the BMS input was re-scaled.
Result
Pressure stability improved to within ±3 Pa, alarms stopped, and the site applied the same change to three more cleanroom zones.
FAQ
HVAC Systems instrumentation questions
What range should I choose for filter differential pressure?
Size the range to roughly twice the fan's maximum static pressure and no more. For a typical AHU that means 0-500 Pa or 0-1,000 Pa; for a cleanroom cascade use 0-100 Pa or 0-50 Pa.
4-20 mA or 0-10 V for a BMS?
4-20 mA over any distance beyond a few metres, because it is immune to cable resistance and detects a broken wire as a zero reading. 0-10 V is acceptable inside a panel but degrades on long runs.
How accurate is a clamp-on flow meter for chilled water?
Around ±2% of reading when the straight run and pipe data are correct, which is adequate for energy allocation but not for billing. For billing-grade heat metering use an inline electromagnetic or ultrasonic meter with EN 1434 approval.
Why does my duct temperature sensor read high?
Usually radiant heat from the duct wall or a sensor that is too short for the duct depth. Use a probe that spans at least a third of the duct depth and mount it away from the heater battery and the corner.
Can your sensors talk to a building management system directly?
Selected models offer native Modbus RTU and BACnet MS/TP. For analogue-only devices we supply a Modbus gateway that presents multiple inputs as one register map, which is often cheaper than replacing the sensors.
Other industries
Send the application details and get a specification back within one business day.