I was recently asked by my manager to help identify this component for a board repair. At the moment, I only have a photo of the part, so I don’t yet have access to the board to take measurements or check it with a multimeter.

The component is from a heater controller board — specifically a Watlow PM8C1EC-AAAAAAA — and the part itself is labeled “DTR.”

Any insight on what this component might be would be greatly appreciated. Thanks!

 

looks like fuse but it could be something else too. once you get the board take good picture of front and back.

https://www.littelfuse.com/products...ace-mount-fuses/nano-2-fuses/415/0415001-drsp
https://www.digikey.ca/en/products/..._a8LumW3eUjgtN_9Pcn5J5Knl2naHn3UaAktHEALw_wcB
https://www.rapidonline.com/schurter-3403-0173-11-umt-smd-fuse-3x10-1mm-time-delay-5a-26-3016

 

The MOSFET immediately to the right of the "DTR" part doesn't look too healthy, though the picture is very blurred. There appears to be a small hole/pit in the centre and some discolouration on the surface which could suggest an overheated or blown part.

 

The 'DTR' part might be a current shunt rather than a fuse...

 

Edit: Oops, sorry. Wrong component.

I should read slower.

If you're talking about the orange part, Google says:

The selected component is a [TE Connectivity Schrack RTD34024](https://www.te.com/en/product-3-1419108-8.html) General Purpose Power PCB Relay. [1, 2]
## Technical Specifications

* Coil Voltage: 24 VDC
* Contact Arrangement: 1 Form A (SPST-NO) (Single Pole Single Throw, Normally Open)
* Current Rating: 16 A switching current
* Rated Voltage: 250 VAC switching capability
* Coil Resistance: 1.44 kΩ ($\pm10\%$)
* Coil Power Consumption: 400 mW nominal
* Environmental Protection: RTIII (Wash-tight enclosure category)
* Mounting Style: Through-Hole (THT) with 5mm pinning layout [1, 3, 4, 5, 6, 7]

## Physical Dimensions

* Length: 29.0 mm
* Width: 12.7 mm
* Height: 15.7 mm [1]

## Procurement & Industry Use
This series is widely integrated into industrial controls, timers, automation equipment, and boiler controllers. Standard replacement parts can be sourced globally from major electrical component distributors like [DigiKey](https://www.digikey.com/en/products/detail/te-connectivity-potter-brumfield-relays/RTD34024/1128669), [Mouser Electronics](https://www.mouser.com/ProductDetail/TE-Connectivity-PB/RTD34024?qs=h4sDRd%2FXtth8Yhy4pibwmw%3D%3D), and [Farnell](https://uk.farnell.com/schrack-te-connectivity/rtd34024/power-relay-spst-no-16a-250v-th/dp/2748038). [2, 8, 9, 10, 11]

[RTD34024 TE Connectivity | TE Connectivity PCB Power Relay ...](https://sa.rsdelivers.com/product/te-connectivity/rtd34024/te-connectivity-pcb-mount-power-relay-24v-dc-coil/6803940), RS Components
[RTE24024 TE CONNECTIVITY - SCHRACK, General Purpose Relay ...](https://www.newark.com/schrack-te-connectivity/rte24024/relay-dpdt-250vac-8a/dp/17M9933), Newark Electronics
[RT314F05 TE Connectivity | TE Connectivity PCB Power Relay ...](https://sa.rsdelivers.com/product/te-connectivity/rt314f05/te-connectivity-pcb-power-relay-5v-dc-coil-16a/1614496), RS Components
[RT33K024 Power Relay 24V 16A TE Connectivity :: SM Elektronik](https://sm-elektronik.eu/index.php?p5027,rt33k024-power-relay-24v-16a-te-connectivity), SM Elektronik
[Schrack RT314524 Relay (ben1) | eBay](https://www.ebay.com/itm/275757465022), eBay
[1 PC) RTE24005 TE RELAY GEN PURPOSE DPDT 8A 5V | eBay](https://www.ebay.com/itm/225561381391), eBay
[RT424F24 TE CONNECTIVITY - SCHRACK, Power Relay, DPDT, 24 VDC ...](https://il.farnell.com/schrack-te-connectivity/rt424f24/relay-dpdt-250vac-8a/dp/1175086), Farnell Israel
[260PCS TYCO RT424615 Power Relay 8A 250VAC 8Pins | eBay](https://www.ebay.com/itm/115467899634), eBay
[SCHRACK RT424024 24VDC](https://wellgainelectronics.com/pcb-relays/28438-schrack-rt424024-24vdc.html), Well Gain Electronics
[The Difference Between Electromechanical and Solid State ...](https://control.com/technical-articles/differences-between-electromechanical-and-solid-state-relays/), Control.com
[5 PCS RT314024 24VDC 16A 24V Relay](https://cityoflakewood.us/listing/5-pcs-rt314024-24vdc-16a-24v-relay?srsltid=212610408), City of Lakewood
[RT314006 | TE Connectivity PCB Power Relay, 6V dc Coil, 16A ...](https://twen.rs-online.com/web/p/power-relays/6803735), RS

If you are diagnosing or replacing this component, tell me:

* What symptoms or malfunctions is the circuit board showing?
* Have you tested the coil with a multimeter to verify its internal resistance?

I can provide diagnostic steps to confirm if the relay has failed.

[1] [https://www.te.com](https://www.te.com/en/product-3-1419108-8.html)
[2] [https://www.mouser.com](https://www.mouser.com/ProductDetail/TE-Connectivity-PB/RTD34024?qs=h4sDRd%2FXtth8Yhy4pibwmw%3D%3D)
[3] [https://sg.element14.com](https://sg.element14.com/schrack-te-connectivity/rtd34024/power-relay-spst-no-16a-250v-th/dp/2748038)
[4] [https://docs.rs-online.com](https://docs.rs-online.com/2e70/A700000007238306.pdf)
[5] [https://www.te.com](https://www.te.com/en/product-1-1393243-0.html)
[6] [https://in.rsdelivers.com](https://in.rsdelivers.com/product/te-connectivity/rtd34024/te-connectivity-pcb-power-relay-24v-dc-coil-16a/6803940P)
[7] [https://www.farnell.com](https://www.farnell.com/datasheets/1869190.pdf)
[8] [https://www.mouser.com](https://www.mouser.com/ProductDetail/TE-Connectivity-Schrack/RTE24024?qs=no2tHrF3Eb29p1pIXPhMgA%3D%3D)
[9] [https://my.mouser.com](https://my.mouser.com/ProductDetail/TE-Connectivity-PB/RTD34024?qs=h4sDRd%2FXtth8Yhy4pibwmw%3D%3D)
[10] [https://www.digikey.com](https://www.digikey.com/en/products/detail/te-connectivity-potter-brumfield-relays/RTD34024/1128669)
[11] [https://uk.farnell.com](https://uk.farnell.com/schrack-te-connectivity/rtd34024/power-relay-spst-no-16a-250v-th/dp/2748038)[\S]

 

looks like fuse but it could be something else too. once you get the board take good picture of front and back.

https://www.littelfuse.com/products...ace-mount-fuses/nano-2-fuses/415/0415001-drsp
https://www.digikey.ca/en/products/..._a8LumW3eUjgtN_9Pcn5J5Knl2naHn3UaAktHEALw_wcB
https://www.rapidonline.com/schurter-3403-0173-11-umt-smd-fuse-3x10-1mm-time-delay-5a-26-3016

I was able to get a hold of the component, and I am pretty sure it is a fuse as you mentioned. There is no resistance across it, and it's shorted both ways (flipped polarity to see if it could possibly be a diode). Thank you!

 

I was able to get a hold of the component, and I am pretty sure it is a fuse as you mentioned. There is no resistance across it, and it's shorted both ways (flipped polarity to see if it could possibly be a diode). Thank you!

This is my second try: according to Google, the part is a shunt:

This component is a high-precision, low-resistance metal strip current sense shunt resistor manufactured by Isabellenhütte. [1]

Component Breakdown

• Brand & Series Identification: The unique physical construction—a central metal alloy resistive element welded directly to two distinct raised tinned copper terminal blocks—is characteristic of Isabellenhütte's high-power surface-mount shunt series (such as the DCR or DTR custom families).
• Marking Meaning: The "DTR" text stamped on the surface is a custom manufacturing or code marking indicating the specific alloy blend, low-ohmic resistance value (typically in the milliohm range), and tolerance rating.
• Primary Function: Unlike standard thin-film resistors used for voltage division, this component acts as a current sensor. By dropping a tiny, precise voltage as current passes through it, it allows nearby power management ICs to calculate and monitor real-time current flow. [1, 2, 3, 4, 5, 6]

-----------

Knowing this component sits inside a Watlow PM8C1EC-AAAAAAA (EZ-ZONE PM Express 1/8 DIN Controller) narrows down its exact function and electrical behavior.

Circuit Location and Role
The PM8C1EC-AAAAAAA variant features a 100-240 VAC universal power input, a mechanical relay output (Output 1), and a switched DC output (Output 2).

• Current Limiting & Fault Monitoring: This Isabellenhütte current sense shunt resistor is strategically placed on the internal power/output stage. It protects the controller's logic boards from current spikes or short-circuits driving the switched DC or relay logic.
• Failure Context: Shunt resistors like this are highly resilient. If this resistor shows visual burning, discoloration, or open-circuit failure, it is a secondary symptom. The primary root cause is almost always a catastrophic short-circuit or over-current event downstream on Output 1 or Output 2, which blew the switching transistor next to it. [1, 2]

Replacement and Repair Path
Because Isabellenhütte prints custom industrial part tracking text ("DTR") on components sold directly to OEM manufacturers like Watlow, you cannot purchase this identical labeled part code from consumer electronic retailers. [1]
To safely bypass or replace it:

1. Measure Across the Elements: Use a high-accuracy micro-ohmmeter or a standard multimeter in resistance mode across the two large solder tabs. A functional shunt will read incredibly close to 0.00 \(\Omega \) (typically between \(1\text{ m}\Omega\) and \(10\text{ m}\Omega\)). If it reads open loop (\(\text{OL}\)), it must be replaced.
2. Sourcing Alternatives: If open, source a general Isabellenhütte SMD current sense resistor of identical physical footprint sizing (e.g., standard SMD 2512 or similar metric footprint) with a sub-10 milliohm value rating matching the control board trace width. [1]

----------------

Because this board contains custom proprietary OEM components, the exact internal schematic values and individual component ratings are omitted from the publicly available Watlow EZ-ZONE PM user documentation. [1]
However, we can cross-reference the physical package design, the stamping format of Isabellenhütte, and the electrical specifications of the Watlow PM8C1EC-AAAAAAA architecture to determine its actual properties.

1. Resistor Value Determination

• Nominal Resistance: This specific layout utilizes an Isabellenhütte SMT series (2817 chip size) design. The lettering format identifies "DTR" as a custom resistance bin code rather than a standard commercial value marking. In this precise sub-circuit application for Watlow, the nominal value is 0.010 \(\Omega \) (10 m\(\Omega \)) or 0.005 \(\Omega \) (5 m\(\Omega \)).
• Power Rating: Based on the standard 2817 SMT package scale from Isabellenhütte, this component features a continuous power rating of 5 Watts to 7 Watts at \(70^{\circ }\text{C}\). [1, 2, 3, 4]

2. Circuit Logic Derivation
We can mathematically deduce the circuit limitations using the electrical constraints of the controller:

• The Controller Output: Your specific model code variant ends in -AAAAAAA. According to Watlow's hardware manual, Output 2 is a Switched DC / Open Collector output.
• The Max Current Rating: Watlow rates this switched DC channel to deliver a maximum of 30mA to 40mA at 24VDC, but features short-circuit clamp protection that triggers if a load demands excessive current.
• The Sense Voltage Target: Modern current-sense logic ICs are designed to trigger fault thresholds when the differential voltage drop across the shunt hits exactly 100 mV to 200 mV.
• The Calculation: By applying Ohm’s Law (\(R = \frac{V}{I}\)):
  \(\frac{0.1\text{\ V}}{10\text{\ A\ (Fault\ Peak)}}=0.010\ \Omega \ (10\text{\ m}\Omega )\)This calculation aligns perfectly with the standard 10 m\(\Omega \) profile of the Isabellenhütte SMT series portfolio. [1, 2, 3, 4]

How to Proceed with Testing
If you suspect the component is faulty, do not rely on standard multimeter test probes to read it in-circuit. Because the resistor sits below \(1\ \Omega\), standard probe lead resistance will mask a correct readout.
Instead, perform a voltage drop test: power the board up safely under normal resting state and measure the millivolt (\(\text{mV}\)) drop across the two tinned solder blocks. If you see a voltage reading exceeding \(0.5\text{ V}\) across it, the resistor has blown open-circuit.
If you are replacing the part, you can swap it safely with a generic Isabellenhütte SMT-R010-1.0 10 m\(\Omega \) 7W 2817 SMD resistor. [1]
Would you like help identifying the adjacent switching transistor part number to check if it was damaged during the same electrical fault?

 

pretty sure that is not 2817. neither length not aspect ratio match.
using optocoupler on the left and 0.1" pitch, or DPACK to the right, this component is 400mil long and perhaps 100mil wide. so package is more like 4010, 4012 or such...

there is a 4014 size but it seem to be for LEDs only.

if it is a fuse, there are products in size 4012 like Littlefuse 250V Nano2® 443 series.
if it is an MOV, it would be different shape (fat/thick) and not connected in series but parallel across voltage lines. also it would be high resistance (they fail short but then explode)
if it is a shunt, there will be two additional thin traces connecting to it, hence we need those pictures to confirm.

most likely it is a fuse or shunt... both of them will have very low resistance when ok.






also checked for all resistors on Isabellenhütte website. there is plenty of shunts but not one of them has form or appearance of product in question:
https://www.isabellenhuette.com/solutions/products?product_area-Resistor=true

DTR it could be an OEM mark too... but interestingly Littelfuse parts may contain DR and DTR... maybe the part is upside down


don't have a side view but shadow suggest DTR is taller than DPACK. that is common for fuses - body cross section is more of a square while resistors are rather flat.
in this image top row are fuses, rest is resistors. note that fuses in ceramic bodies have over the body caps for terminal (larger than body)



no AI was used in this post...

 

pretty sure that is not 2817. neither length not aspect ratio match.
using optocoupler on the left and 0.1" pitch, or DPACK to the right, this component is 400mil long and perhaps 100mil wide. so package is more like 4010, 4012 or such...

there is a 4014 size but it seem to be for LEDs only.

if it is a fuse, there are products in size 4012 like Littlefuse 250V Nano2® 443 series.
if it is an MOV, it would be different shape (fat/thick) and not connected in series but parallel across voltage lines. also it would be high resistance (they fail short but then explode)
if it is a shunt, there will be two additional thin traces connecting to it, hence we need those pictures to confirm.

most likely it is a fuse or shunt... both of them will have very low resistance when ok.

View attachment 367256

View attachment 367261

also checked for all resistors on Isabellenhütte website. there is plenty of shunts but not one of them has form or appearance of product in question:
https://www.isabellenhuette.com/solutions/products?product_area-Resistor=true

DTR it could be an OEM mark too... but interestingly Littelfuse parts may contain DR and DTR... maybe the part is upside down
View attachment 367259

no AI was used in this post...

Thanks for the non-AI response haha. I did notice Littlefuse has similar naming conventions. I think my next step would be finding a multimeter back at our shop that has the capability to measure small resistance... Besides that, my best guess is that Littlefuse made something like this at some point in the past, but now it is discontinued, apparently these heater controllers have been in the company I am working at for quite some time, and now discontinued... hence trying to fix them rather than just ordering new ones.

Thanks again for your detailed responses. I really appreciate it!

 

unfortunately that PCB has no silkscreen for additional clues. i would try to locate any IC nearby and check if there is a continuity from DRT to it and if so, determine to how many IC pins.
if it is zero or one pins, this is a fuse. if it is two (likely side by side) pins, this is a shunt. for this to be shunt that casts wide shadow, it would need to have center of the body raised above PCB.
for example:

 

unfortunately that PCB has no silkscreen for additional clues. i would try to locate any IC nearby and check if there is a continuity from DRT to it and if so, determine to how many IC pins.
if it is zero or one pins, this is a fuse. if it is two (likely side by side) pins, this is a shunt. for this to be shunt that casts wide shadow, it would need to have center of the body raised above PCB.
for example:
View attachment 367264

My manager was able to bring the piece to the track but not the board (we are not at our regular shop at the moment). It is a solid, non-raised piece. Once we are back at our shop I will probe around and check the connections, I am fairly certain if this is indeed a fuse, that mosfet probably went bad too.

 

@panic mode It would be very unusual to have packaging coding on the item, you wouldn't know at time of manufacture how it would be packaged. My guess is DTR is either the manufacturer or branding.