reTerminal-DM touchscreen unstable when powered from industrial 24 V supply, works only when touching chassis

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1

I am using a reTerminal DM with injection molding machine and facing unstable capacitive touch behavior.

Symptoms:

  • Screen randomly zooms in/out

  • Touch position shifts

  • Touch becomes stable only when I physically touch the reTerminal chassis with my hand

  • Issue appears when powered from Mean Well mdr-60-24 power supply.

This suggests a grounding or common-mode noise issue affecting the capacitive touch controller.

Power setup

Power supply used:

Mean Well MDR-60-24 (DIN-rail SMPS)

Connections made:

  • L/N connected to machine single-phase supply

  • +24 V / −24 V connected to reTerminal DM

  • V− bonded to panel PE

  • reTerminal chassis bonded to panel PE

  • MDR-60-24 FG bonded to panel PE

Despite these connections, issue persists.

Measurements

Measured AC voltage between:

MDR-60-24 V− and panel PE ≈ 60 V AC (before grounding changes)

After bonding FG and V− to PE, behavior improved slightly but touchscreen instability still remains.

Touch becomes stable immediately when:

I touch chassis with my hand

which suggests missing reference stabilization or high common-mode noise in cabinet environment.

Machine environment

Installation is inside an injection molding machine panel containing:

  • hydraulic motor contactors

  • possible VFD drives

Cable length between PSU and reTerminal is short (<2 m).

Tests already performed

Tested:

  • bonding V− to PE

  • bonding FG to PE

  • bonding chassis to PE

  • verifying continuity of panel earth

Questions

  1. Is reTerminal DM known to require isolated supply in industrial control panels?

  2. Does Seeed recommend grounding output negative to PE or keeping it floating?

  3. Are there any official EMC mitigation guidelines for capacitive touch stability in noisy cabinets?

  4. Has anyone successfully deployed reTerminal DM with injection molding or CNC panels without isolated DC-DC stage?

2

Hi there,

SO, on the IO/ panel isn’t there an ISO/GND pin , used on the canbus often too.
it’s the dedicated isolated pin on the reTerminal, I was under the impression. I think also a post of another maker using it similar too , the isolation for power supply GND (noise) issue for your use case FAIK.

HTH
GL :slight_smile: PJ :v:

3

Hi @PJ_Glasso

I tried following connection: Injection Molding panel earth to Negative of the meanwell MDR-60-24 power supply output and ran a short wire to connect panel earth to reterminal-dm earth [Above the power supply port]

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As per your suggestion, should I connect injection molding machine panel earth to GND_ISO?

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Because this earthing issue is causing touch screen instability [zoom in/out, ghost touch] and is not usable at all. Should I also reach out to seeedstudio team for the same?

4

Hi there,

Ok, YES absolutly . Connect it and report back, You can’t hurt anything so no worries there.
if possible can you measure your power supply AC ripple component. if it’s too noisy , find a higher working voltage CAP and nothing huge 20 uf. see if it lowers it a bit in the meter, (ac settings) checking the DC supply. note the reading, add the cap ..note the reading. Any change if so try the reTerminal again.

HTH
GL :slight_smile: PJ :v:

I have had some super crazy noise enviro’s before, one was a motor for an overhead crane… when that thing kicked into gear and moved , it would spike the AC around the whole neighborhood it seemed :grin: We added Heavy Isolation and split filtered the mains supplied to it. added some additional CAPs to the power supply for the servos and MMI display power legs, and life was good again. :crossed_swords:

5

Hi @PJ_Glasso

There are some improvements from last time, as stated earlier reterminal DMs were connected to total 19 injection molding machines and is used for real-time data acquisition from injection molding controllers and HMIs using LAN and RS485 (In few controllers).

Earthing was refreshed and connections were re-checked, BUT the bad news is still there was issue with touch sensitivity with ghost touches, zoom etc. For a quick test I also removed AC power supply from meanwell SMPS and connected battery UPS and still there was this touch issue. I also replaced temporary omron power supply with meanwell one but this didn’t help.

As you suggested I tried reading AC ripple on power supply (SMPS) output but my UNI-T meter didn’t gave any reading! So for final solution I connected power line EMI/EMC filter with ground connected to earthing and reterminal DM screen worked correctly!

Now for final solution, I will be purchasing good quality power line EMI/EMC filters TDK make and call it a day until something comes up in future.

What’s your take on this problem? Is it a very different case of EMI/EMC or something related to quality/harmonics of AC power supply?

6

Hi There,

Anshuman,
That is absolutely fantastic news! I am glad to hear that adding the EMI/EMC filter completely stabilized the touchscreen. You can officially mark that down as the solution!
:grin: :+1:

To answer your question: what you are experiencing is actually a very classic case of heavy industrial EMI/RFI, rather than just a simple issue of AC ripple or power supply quality.

Because you are deployed across 19 injection molding machines with long LAN and RS485 data lines, your entire setup is essentially sitting in a massive web of high-frequency common-mode noise. This noise is generated by the massive inductive loads (like heater bands, motors, and hydraulic pumps) switching on and off.

Why the Filter Solved It:

  • The UPS Test: When you ran it on a battery UPS and the issue persisted, it proved that the noise wasn’t just coming from the AC mains into the SMPS.

  • The Real Culprit: The high-frequency noise is likely being radiated through the air or induced directly onto your communication lines and the machine’s massive metal chassis.

  • The Shunt: Capacitive touchscreens (like the one on the reTerminal-DM) are incredibly sensitive because they rely on detecting tiny changes in capacitance relative to earth ground. When you added the power line EMI/EMC filter and tied its ground to earthing, you created a low-impedance path that shunts all that high-frequency stray noise safely away to ground before it can confuse the touchscreen controller.

A Quick Tip Moving Forward:

Going with high-quality TDK filters is an excellent permanent choice—they make great industrial-grade components. When you install them permanently, just try to keep the wire runs between the TDK filter and the reTerminal-DM as short as possible. If those wires are too long, they can act like little antennas and pick up the radiated noise all over again.

Awesome troubleshooting job sticking with it and finding the root cause. Enjoy the flawless screens!

GL :slight_smile: PJ :hammer_and_wrench:

7

Thanks @PJ_Glasso marked this solution as solved! I hope seeedstudio can consider this in design for future upgrades in other products which are industrial environment oriented!