HM SERIES — ELECTRONIC PRESSURE SWITCH

HM41 Compact Electronic Pressure Switch

The HM41 is a compact electronic pressure switch co-developed with German HELM, combining microprocessor-controlled pressure measurement, 4-digit LED display, and dual relay output in a single instrument. With ±0.1% FS accuracy and adjustable set points across the full range, it delivers precise switching control from vacuum to 100 MPa — ideal for equipment automation, hydraulic systems, and industrial process control.

100 MPa

Max Range

±0.1% FS

Accuracy

Dual Relay

Switch Output

IP65

Protection

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Product Overview

The HM41 Compact Electronic Pressure Switch is an intelligent digital switching instrument that integrates pressure measurement, real-time display, and relay control in a single compact housing. Co-developed with German HELM, it utilizes HELM’s proprietary high-stability sensing elements and advanced microprocessor-based signal processing to deliver reliable switching performance across a wide range of industrial conditions.

Unlike traditional mechanical pressure switches that rely on spring-loaded diaphragms with limited accuracy and repeatability, the HM41 employs a piezoresistive sensor with digital signal conditioning. This enables freely adjustable set points across the full measuring range, with anti-chatter hysteresis settings to prevent rapid cycling. The dual relay outputs (each with both NO and NC contacts) support independent alarm thresholds, making it suitable for both low-pressure and high-pressure alarm configurations simultaneously.

The instrument features a 4-digit LED display for real-time pressure reading, multiple power supply options (24 VDC, 220 VAC, 380 VAC), and optional analog (4–20 mA, 0–5 VDC) or digital (RS485) signal output. Built with robust surge protection, reverse-polarity protection, and strong EMI resistance, the HM41 is engineered for demanding automation environments where accurate, repeatable pressure switching is critical.

Technical Specifications

Parameter	Specification
Measuring Range	Vacuum: 0 to −100 kPa; Gauge: 0 to 100 MPa; Absolute: 0 to 3.5 MPa; Compound: −100 kPa to 20 MPa
Pressure Type	Gauge, Absolute, Differential
Overload Capacity	1.5× FS (1.1× FS for 100 MPa range)
Overall Accuracy	±0.1% FS / ±0.25% FS / ±0.5% FS / ±1% FS (selectable)
Long-Term Stability	Typical: ±0.2% FS; Max: ±0.5% FS
Switch Output	Dual relay (each with NO + NC contacts); set points adjustable across full range
Relay Load Rating	220 VAC / 5 A; 24 VDC / 5 A
Signal Output (Optional)	4–20 mA / 0–5 VDC (analog); RS485 (digital, custom)
Display	4-digit LED digital display
Sampling Rate	10 Hz
Power Supply	24 VDC / 220 VAC / 380 VAC (custom)
Operating Temperature	−10 to 70°C (high-temp custom available)
Wetted Materials	304 Stainless Steel (body & process connection)
Process Connection	M20×1.5, G1/4, custom
Electrical Connection	Lock-head direct cable (0.3 m); 8-pin aviation connector (0.3 m)
Panel Diameter	Ø100 mm / Ø80 mm / Ø60 mm / custom
Mounting	Radial (default) or Axial
Protection Grade	IP65
Weight	Approx. 0.5 kg
Compatible Media	Gases and liquids compatible with 316 stainless steel

Key Features

Dual Relay Output with NO+NC

Two independent relay channels, each providing both normally-open and normally-closed contacts. Supports simultaneous high/low alarm thresholds rated at 220 VAC / 5 A and 24 VDC / 5 A for direct load switching.

Freely Adjustable Set Points

Alarm thresholds can be set to any value within the full measuring range via front-panel buttons. Anti-chatter hysteresis is user-configurable to prevent rapid relay cycling near the set point.

4-Digit LED Real-Time Display

Bright 4-digit LED panel shows live pressure readings with 10 Hz update rate, enabling operators to monitor process pressure at a glance without additional display instruments.

German HELM Sensing Technology

Utilizes HELM’s high-precision, high-stability piezoresistive sensing elements with excellent corrosion resistance, shock tolerance, overload protection, vibration resistance, and long-term stability.

Multiple Power & Output Options

Supports 24 VDC, 220 VAC, or 380 VAC power supply. Optional analog output (4–20 mA, 0–5 VDC) or RS485 digital output enables integration with PLCs, SCADA systems, and data loggers.

Robust Industrial Protection

IP65-rated stainless steel housing with built-in surge protection, reverse-polarity protection, and strong EMI resistance. Available in Ø60, Ø80, and Ø100 mm panel sizes with radial or axial mounting.

Applications

Equipment Automation

Provides precise pressure-based on/off control for automated machinery, CNC equipment, and production lines. The dual relay outputs enable independent high and low pressure alarms for equipment protection.

Hydraulic & Pneumatic Systems

Monitors hydraulic and pneumatic circuit pressure with configurable set points to trigger pump start/stop, valve actuation, or safety shutdowns. The 100 MPa range covers high-pressure hydraulic applications.

Pump & Compressor Control

Automates pump and compressor start/stop based on system pressure thresholds. The hysteresis setting prevents short-cycling, extending equipment life and reducing energy consumption.

Energy & HVAC Systems

Controls heating and cooling system pressure for boilers, chillers, and district heating networks. Multiple power supply options (24 VDC, 220 VAC, 380 VAC) match diverse HVAC electrical standards.

Medical Equipment

Provides reliable pressure switching for medical gas systems, sterilization chambers, and pneumatic instruments where ±0.1% FS accuracy ensures patient safety and regulatory compliance.

Pressure Test Laboratories

Serves as a digital pressure indicator with switching capability in calibration labs and test benches. The LED display and optional analog/RS485 output support both visual monitoring and data acquisition.

Ordering Guide

Use the model code below to specify your HM41 configuration. Example: HM41 (0~100 kPa) — 1 — V2 — D2 — F1

Code	Options
Pressure Type	-G: Gauge (default); -A: Absolute; -D: Differential
Range	Specify measuring range, e.g., 0~1 MPa
Accuracy	0: ±1% FS; 1: ±0.5% FS; 2: ±0.25% FS; 3: ±0.1% FS
Power / Display	V2: 24 VDC + LED; V3: 220 VAC + LED; V4: 380 VAC + LED (custom)
Panel Size	D1: Ø100 mm; D2: Ø80 mm; D3: Ø60 mm; D0: Custom
Process Connection	F1: M20×1.5; F2: G1/4; F0: Custom
Electrical Connection	W1: Lock-head direct (0.3 m cable); W2: 8-pin aviation connector (0.3 m cable)
Additional Options	J: Radial mount (default); Z: Axial mount; S: Analog signal output; P: Engineering plastic housing

HM40 Digital Pressure Gauge

Display-only version without relay switching. Choose the HM40 when you need precision digital pressure indication with peak value recording and no switching control.

HM200E Wireless Digital Pressure Gauge

Wireless upgrade with LoRa communication and cloud monitoring. Ideal when you need remote pressure data without running cables to every measurement point.

HM24 Low Cost Pressure Transmitter

Budget-friendly transmitter with digital display and standard 4–20 mA output. Choose the HM24 when you need continuous analog signal without relay switching functionality.

Frequently Asked Questions

The HM41 and HM40 share the same sensing platform and display but serve different functions. The HM41 includes dual relay outputs (each with NO+NC contacts) for automated on/off control, making it a true pressure switch with display. The HM40, on the other hand, is a display-only instrument designed for precision pressure indication and peak value recording — it does not have relay switching capability. Choose the HM41 when you need automated pressure-based control, and the HM40 when you only need visual monitoring.

The HM41 features front-panel push buttons for configuring both alarm set points. You can set each relay’s trigger threshold to any value within the measuring range, and independently adjust the hysteresis (deadband) to prevent rapid on/off cycling. No external programming tools are needed — all settings are made directly on the instrument. The two relay channels operate independently, allowing you to set a low-pressure alarm on one channel and a high-pressure alarm on the other.

Yes. The HM41 supports optional analog output (4–20 mA or 0–5 VDC) as well as RS485 digital output. When ordered with the “S” option code, the unit can simultaneously provide relay switching control and a continuous analog or digital signal for PLC integration, SCADA monitoring, or data logging. Specify the desired output type when placing your order.

Each of the HM41’s two relay channels is rated for 220 VAC / 5 A or 24 VDC / 5 A resistive load. This is sufficient to directly switch small motors, solenoid valves, indicator lamps, and audible alarms. For higher loads, use the relay output to drive an external contactor or motor starter. Each channel provides both normally-open (NO) and normally-closed (NC) contacts for flexible wiring configurations.

Yes. The HM41 is available with custom measuring ranges, special process connections, extended operating temperature ranges, engineering plastic housing, and axial mounting orientation. Contact our engineering team with your specific requirements — we can customize panel diameter (beyond the standard 60/80/100 mm), add signal outputs, or modify wetted materials for your application. Lead time for standard configurations is typically 5–10 business days; custom orders may require additional time.

Need a Pressure Switch Solution?

Tell us about your application and our engineers will recommend the right HM41 configuration — range, accuracy, power supply, and output options tailored to your process requirements.

Our engineers typically respond within 12 business hours.

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HM SERIES — ELECTRONIC PRESSURE SWITCH

HM41 Compact Electronic Pressure Switch

Product Overview

Technical Specifications