HotLug Watch · joint temperature monitoring for induction furnaces

Every bolted joint.
Every 10 seconds.

Fiber-optic probes on the rectifier, inverter, capacitor and furnace cable connections, and software that finds the loose joint while it is still only warm.

Get a probe plan for your furnace See how it works
One 18-probe module · inverter section°F
Inv 1 · A126.3
Inv 2 · A170.8
Inv 3 · A126.1
Inv 1 · B126.0
Inv 2 · B125.6
Inv 3 · B126.7
Inv 1 · DC+124.5
Inv 1 · DC−122.9
Inv 2 · DC+123.4
Inv 2 · DC−124.2
Inv 3 · DC+122.7
Inv 3 · DC−123.6
DC link 1+127.2
DC link 1−126.1
DC link 2+125.8
DC link 2−127.0
Bus A out127.4
Bus B out125.2
One inverter output runs about 44 °F hotter than its two sisters at the same load. A loosening joint shows up like this weeks before it fails. Illustration.
Fiber-optic probesall-dielectric, right on the joint, unaffected by the furnace field
Every 10 secondsday and night, every heat, not once a year
No cloudruns on one PC on your plant network
Where we measure

The weak point is the joint, not the equipment.

Between the transformer and the coil, a medium-frequency furnace carries thousands of amps through dozens of bolted and clamped joints. When one loosens, it heats with every melt. HotLug Watch puts a probe on each joint that matters.

Stage 1

Rectifiers

AC input connections on every phase, DC output legs on every thyristor.

Stage 2

DC link and inverters

Reactor cable connections, DC + and − at each inverter, outputs at the busbars.

Stage 3

Capacitors and switches

Disconnect and changeover contacts on line and load side, capacitor switches, incoming busbars.

Stage 4

Furnace cables

Water-cooled cable connections, where the current to the coil is highest.

Thyristor or IGBT, parallel or series resonant. Every probe plan is drawn up from your furnace's own electrical drawings.

Why joints fail

  • Melt cycles heat and cool them hundreds of times a week, and bolts lose tension.
  • Contact faces oxidize; a little more resistance means a lot more heat.
  • After maintenance, a joint can go back together with the wrong torque.

Why yearly thermography misses it

  • A joint can go from warm to burnt in weeks, between two surveys.
  • Many joints sit behind covers or are water-cooled, out of a camera's sight.
  • A survey sees one load on one day; a probe sees every heat.
What your crew sees

The hot joint, the reason, and what to do next.

Compared with its sisters

Probes that carry the same current should run alike. One that runs hotter stands out at any load.

Limits you already know

Rise over ambient after NETA MTS, absolute limits after NEC 110.14(C), per connection type.

Rapid rise

A probe heating faster than the others in 10 minutes is flagged at once. All rising together is the melt starting.

Explained in plain words

A local AI explains each finding and writes the shift report. Alarms come from fixed rules; the AI never raises or clears one.

InvertersCritical
Output A
1126.3
2170.8
3126.1
Output B
1126.0
2125.6
3126.7
DisconnectAdvisory
Contacts
A line128.3
A load129.7
B line127.2
B load142.2
Rectifier 1Normal
AC input
A123.6
B124.7
C124.5
CriticalInverter 2, output A: 44.6 °F hotter than similar connections
The joint has run hotter than inverters 1 and 3 at every melt for 10 days, and the gap is growing. Likely a loosening or oxidized connection. Check and re-torque at the next planned stop.
Illustration of the HotLug Watch overview, °F.
How it works

From your drawings to a running system in one planned outage.

  1. 01Send us your electrical drawings. We read the power path from transformer to coil and mark the joints that carry the most current.
  2. 02Probe plan and fixed-price quote within two weeks. Every probe named and placed, every module and fiber run listed.
  3. 03Installation during your next planned outage. Two to three days per furnace, with your electricians, under lock-out/tag-out and NFPA 70E.
  4. 04Three-month pilot with a written report. Baseline, findings and recommendations for your furnace, in a report your team can act on.
  5. 05Service plan. Updates, remote support, a yearly thermal health report and a new baseline after every maintenance.
Industries

Wherever thousands of amps pass through a bolt.

Iron and steel foundries

Medium-frequency induction melting, from the converter to the coil.

Forging and induction heating

Billet heaters and hardening lines with the same power electronics.

Rectifier halls

Large DC rectifiers for electrolysis and electro-processing.

Plating lines

High-current DC busbars and their bolted connections.

Built for the plant

Your data stays in your plant.

HotLug Watch needs no internet connection. It adds analysis to your furnace and never becomes part of its protection.

Probes
Fiber-optic, all-dielectric, unaffected by the medium-frequency field; high-temperature probes for the hottest joints
Modules
18 probes per module, as many modules as the furnace needs, Modbus TCP
Readings
Every 10 seconds; every reading kept 90 days, 5-minute averages 5 years
Runs on
One PC in your plant, opened in any browser on your network; operator, technician and admin roles; °F or °C per user
AI
A language model on the same PC, for explanations, shift reports and questions
Protection
Each module's own alarm relay stays hardwired to your furnace alarm
About HotLug Systems

Built by people who know furnace power systems.

HotLug Systems engineers, installs and supports HotLug Watch for induction furnaces and other high-current systems. Every probe plan starts from the customer's drawings, and every installation is done with the plant's own electricians.

HotLug Systems was founded by Nicolai Zernikow.

Contact

Send us your drawings.

You get a probe plan and a fixed-price quote for your furnace within two weeks.

Nicolai Zernikow (630) 397-9237 nicolai.zernikow@hotlug.com
Drawings can follow by email after we reply.