USB HART Modem (HM1-UD)

The HM1-UD is a portable USB HART modem that connects a PC or laptop to HART field instruments. Use it with PACTware, FieldCare, FieldMate, SIMATIC PDM or any DTM/DD-based software to configure, calibrate, maintain and diagnose HART devices. It plugs straight into a USB port, needs no separate power supply and no serial port.

Why the HM1-UD

• Works with the tools you already use: the driver creates a standard virtual COM port, so the modem drops straight into PACTware, FieldCare, FieldMate, SIMATIC PDM and other HART device managers.
• USB bus-powered: one connection carries data and power (under 0.25 W). Nothing else to plug in.
• Fully isolated: a 2500 V galvanically isolated loop interface protects your PC, and the connection is polarity-independent.
• Truly portable: a compact USB-stick modem with two flexible grabber-clip leads, ideal for the laptop bag, the calibration bench or the field. A USB extension lead can be used for extra reach.
• Point-to-point and multi-drop: acts as a primary or secondary HART master on single-instrument and multi-dropped loops.

What is a USB HART modem?

HART instruments carry digital data on top of their 4–20 mA signal. A USB HART modem converts that signal so a computer can talk to the instrument: read its configuration and diagnostics, change settings and calibrate it. The HM1-UD is a raw modem, so your software handles the HART protocol and the modem passes the signalling through in both directions.

Set up in three steps

1. Plug it in. On an internet-connected Windows PC the driver installs automatically. Otherwise download it from our support site. Drivers have also been produced for macOS and Linux; contact support for those.
2. Clip onto the loop. Connect the two leads across the loop sense resistor or directly across the instrument, either way round. HART needs a loop load of about 250 Ω, which a working 4–20 mA loop normally already has; on the bench, add a resistor.
3. Select the COM port in your device-management software and scan. Most tools apply the HART serial settings (1200 baud, 8-O-1) automatically.

Technical specification

HART interface	1 channel · primary / secondary master · point-to-point & multi-drop
Host interface	USB 2.0 · virtual serial (COM) port via driver · raw modem protocol
Loop connection	Two flying leads with grabber clips · polarity-independent
Isolation	Fully isolated loop interface · 2500 V dielectric (1 minute)
Power	+5 V from the USB port · < 0.25 W
Operating temperature	0 to +50 °C
Storage temperature	−20 to +70 °C
Humidity	0 to 70 % non-condensing
Software	PACTware, FieldCare, FieldMate, SIMATIC PDM and other DTM/DD-based tools

Compliance: CE (EN ISO 17050-1:2004) · FCC Part 15 (Class A) · ICES-003.

Frequently asked questions

Does it need an external power supply?
No. It is powered from the USB port.

Do I need a resistor?
Only if there isn't one already. HART needs about 250 Ω in the loop; installed 4–20 mA loops normally have it, bench set-ups often don't.

Will it find devices on a multi-drop loop?
Yes. Point-to-point devices answer at address 0; set your software to scan addresses 1–15 for multi-dropped loops.

Can I use it with my own software?
Yes. It appears as a standard serial port: RTS switches the modem to transmit, and CTS, DSR, DCD and RI indicate a HART carrier on the loop.

In the box

HM1-UD USB HART modem with two flying leads and grabber clips. The driver installs automatically on Windows or can be downloaded from the support site.

Documentation & downloads

• Product Datasheet
• Quick Start Guide
• User Manual
• Support portal & driver downloads

Warranty & support

12-month hardware warranty (return-to-base repair or replacement); see our returns & warranty policy. Backed by direct engineering support from the team that designs it.