An industrial fluid state sensing device that sends an ON / OFF switch signal to the PLC. This series centers on the Honeywell DPS400 low differential pressure switch (switch point 40–400 Pa), for cleanroom pressure monitoring, HVAC duct pressure sensing, filter clogging detection and semiconductor process gas flow verification.
A pressure switch is a two-state sensing device that tells whether fluid pressure has reached a set value. Unlike a pressure transmitter, which outputs a continuous 4–20 mA analog signal, a pressure switch only outputs ON / OFF. Wiring is simple and cost is low, so it suits places that need an action “when a certain pressure is reached”: filter clogging alarms, compressor start / stop, cleanroom door interlocks and HVAC fan fault monitoring.
This series includes the Honeywell DPS400 differential low-pressure switch with a switch point range of 40–400 Pa, in the low “Pa-level” range. Honeywell has listed the DPS series as discontinued; please ask us about stock and replacement models. For cleanroom pressure differences, USP <797> requires at least 0.02 inch water column (about 5 Pa) between adjacent areas, and the general reference in the ISO 14644-4 annex is 5–20 Pa; this range needs a low differential pressure switch with a lower range (the DPS400 switch point starts at 40 Pa, so choose according to your actual pressure difference). We supply pressure switch spares from Honeywell, Dwyer, SMC and other brands for cleanroom and HVAC maintenance at semiconductor, biotech and SMT plants around Hsinchu Science Park.
Specifications (Honeywell DPS400 example)
| Item | Specification | Note |
|---|---|---|
| Model | Honeywell DPS400 | Representative differential low-pressure switch |
| Pressure type | Differential | Two ports, measures the difference between two points |
| Max. operating pressure | 5,000 Pa (per the manufacturer’s catalog) | Low range, for cleanroom / HVAC |
| Switch point range | 40–400 Pa (switching differential 20 Pa) | Adjustable by knob on site; general case, each case needs checking |
| Sensing element | Silicone rubber diaphragm | High-sensitivity diaphragm for low pressure |
| Output | SPDT | NO / NC contacts selectable |
| Contact rating | 1.5 A / 250 VAC (SPDT changeover contact) | See the datasheet |
| Pressure ports | Two 6 mm hose ports | Do not swap the high and low ports |
| Operating environment | -20 to +85°C | Fine at cleanroom room temperature |
| Mounting | Mainly horizontal | Low-pressure switches are sensitive to gravity; mount as the datasheet specifies |
Applications
In electronics and biotech plants, pressure switches are used mainly in three areas: clean environment pressure monitoring, fluid system fault detection and machine state verification. Common cases in Hsinchu Science Park plants:
- Semiconductor cleanroom pressure: Class 1–100 clean areas in wafer fabs should be kept +10 to +15 Pa above adjacent dirtier areas (gowning rooms, corridors). The differential switch’s two ports connect to the pressure taps in both areas; when the difference drops below the setpoint, the ON / OFF output triggers an alarm so HVAC increases supply air or staff inspect. For cleanroom pressure monitoring, choose a low differential pressure switch with a range suited to the actual difference (the DPS400 switch point starts at 40 Pa).
- HVAC filter clogging detection: HEPA and ULPA filters collect dust over time and the pressure difference across them rises. Connect the DPS400’s two ports to the taps before and after the filter; when the difference exceeds the setpoint (for example 250 Pa), it outputs a replacement alarm to prevent low airflow.
- Process gas line flow verification: a differential switch checks whether the pressure difference across semiconductor CVD, PVD and etcher process gas piping stays within design range and sends an ON / OFF interlock to the PLC, stopping the machine automatically on abnormal pressure to prevent process deviation or scrapped wafers.
- Biotech BSL-2 / 3 lab negative pressure: BSL-2 / 3 biosafety labs should stay at negative pressure to the outside (to keep hazardous material in). A low differential pressure switch monitors room vs corridor pressure (choose the range by the actual difference) and triggers alarms and door interlocks when it goes out of range.
Selection by pressure range and media
| Application | Suggested type | Typical range | Note |
|---|---|---|---|
| Cleanroom area pressure difference | Differential low-pressure switch | 0–500 Pa | Choose range by actual difference (DPS400 switch point 40–400 Pa) |
| HVAC filter clogging | Differential low-pressure switch | 0–500 Pa or 0–1000 Pa | Choose range by fan head |
| Compressed air line ON / OFF | Positive pressure switch | 0–10 bar | Not differential, single port |
| Vacuum line level check | Negative / vacuum switch | -100 to 0 kPa | Single port on the vacuum side |
| High-pressure process gas monitoring | Positive pressure switch | Depends on the process | Check corrosion-resistant materials |
Three switch types: first know what you are measuring
There are three types of pressure switch; the difference is what reference the pressure is measured against:
| Type | Measures | Ports | Typical range | Typical use |
|---|---|---|---|---|
| Differential | Difference between two pressures | 2 (high / low) | 0–500 Pa to 0–10 kPa | Cleanroom pressure, filter clogging |
| Gauge / positive | Pressure vs atmosphere | 1 | 0–1 bar to 0–100 bar | Compressed air, process gas, hydraulics |
| Vacuum | Vacuum vs atmosphere | 1 | -100 to 0 kPa | Vacuum cups, vacuum grippers, exhaust systems |
A common mistake: do not confuse pressure difference with pressure. A cleanroom area might be at +101.310 kPa (10 Pa above atmosphere); a positive pressure switch sees about 101 kPa fluctuating and cannot see a 10 Pa difference at all. You must use a differential switch to measure the 10 Pa between the clean area and the corridor.
The product on this page is the Honeywell DPS400 differential low-pressure switch; positive and vacuum types are available on request.
Five selection steps
In practice, selection does not start with “which brand”; work through these five steps:
- Confirm what you measure: a difference between two points, pressure vs atmosphere, or vacuum level.
- Estimate the actual pressure range: choose a range 1.5–3 times the actual value (margin to avoid damage).
- Check the units: Pa for cleanroom / HVAC; bar for pneumatics / hydraulics; kPa for vacuum.
- Check media compatibility: clean air, process gas, liquid or corrosive gas each need the right diaphragm material.
- Confirm the contact rating: low rating for a PLC digital input; higher rating to drive relays or alarms.
Practical tips: 4 things to confirm when buying and installing
- Label the high and low ports before installing: a differential switch connected backwards will not switch or will switch the wrong way, which often happens when a replacement goes online without checking. Label the ports clearly and test with a hand bulb before connecting the piping.
- Low-pressure (Pa-level) switches are very sensitive to gravity: the diaphragm zero shifts between horizontal and vertical mounting. Low-pressure types such as the Honeywell DPS400 are mainly mounted horizontally; follow the datasheet, or zero drift will cause false switching.
- Set hysteresis to avoid chatter: leave a 20–50% gap between the switch point and the reset point (for example switch at 50 Pa, reset at 30 Pa) so the relay does not chatter when pressure hovers at the limit, which can extend service life; whether hysteresis can be adjusted on site depends on the manufacturer’s catalog.
- Keep spares for cleanroom / HVAC: if a cleanroom pressure fault or filter alarm cannot be read, production is directly affected.
The ranges and switch point suggestions above are common industry values; follow the datasheet, and each case still needs to be checked.
How to request a quote: please send (1) the model or the pressure type and range; (2) the media; (3) the quantity; (4) how urgent it is.
Trademarks: Honeywell, Dwyer, SMC and the model names on this page are trademarks or model names of their owners, used here only to identify the products. JIAHON is not the authorized distributor of these brands in Taiwan.
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