Termination Resistor: Power Rating 0.25W to 1W

Component Specifications

Definition

A termination resistor is a passive electronic component installed at both ends of an RS485 communication bus to match the characteristic impedance of the transmission line, typically 120 ohms. It absorbs signal energy at the line ends, preventing reflections that cause data corruption, signal distortion, and communication errors in industrial networks.

Working Principle

The termination resistor works by matching the characteristic impedance of the transmission line (typically 120Ω for RS485). When installed at both ends of the bus, it absorbs signal energy that reaches the line ends, preventing signal reflections. This maintains signal integrity by ensuring clean voltage transitions and preventing standing waves that can cause data errors in differential communication systems.

Materials

Typically composed of carbon film, metal film, or thick film resistive material on ceramic substrate, with tin-plated copper leads or surface mount terminations. Housing materials include epoxy coating or ceramic packaging for industrial environments.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Tolerance	±1% to ±5%
Resistance	120Ω ±1%
Package Type	Through-hole (axial/radial) or Surface Mount (SMD)
Power Rating	0.25W to 1W
Operating Temperature	-40°C to +125°C
Temperature Coefficient	±100 ppm/°C

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 11898, TIA/EIA-485-A, IEC 61158

Parent Products

This component is used in the following industrial products

RS485 Communication Module

A hardware module that implements the RS485 serial communication standard for industrial data transmission.

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Engineering Analysis

Risks & Mitigation

Incorrect resistance value causing impedance mismatch
Overheating due to insufficient power rating
Corrosion in humid environments
Mechanical failure from vibration
Incorrect placement (not at both bus ends)

FMEA Triads

Trigger: Open circuit due to mechanical stress or corrosion
Failure: Complete loss of termination, causing severe signal reflections and communication failure
Mitigation: Use vibration-resistant mounting, conformal coating, and regular impedance testing

Trigger: Resistance drift from temperature extremes or aging
Failure: Impedance mismatch leading to intermittent communication errors
Mitigation: Select resistors with low temperature coefficient and derate power usage

Trigger: Short circuit from contamination or insulation breakdown
Failure: Bus loading and potential damage to transceivers
Mitigation: Proper sealing, clean installation environment, and current limiting protection

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

±1% resistance tolerance recommended for industrial applications

Test Method

Impedance verification using LCR meter at 1MHz, continuity testing, and thermal cycling per IEC 60068-2-14

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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Manufacturers of Termination Resistor

Manufacturer profiles associated with Termination Resistor.

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review

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Frequently Asked Questions

Why is a 120 ohm resistor used for RS485 termination?

120 ohms matches the characteristic impedance of typical twisted pair cables used in RS485 networks, providing optimal signal integrity by minimizing reflections at the bus ends.

What happens if termination resistors are missing in an RS485 network?

Without termination resistors, signal reflections occur at bus ends, causing data corruption, communication errors, reduced maximum cable length, and potential system instability.

Can I use a different resistance value for RS485 termination?

No, using values significantly different from 120Ω creates impedance mismatch. Some systems use 100-150Ω with specific cables, but 120Ω is the standard per TIA/EIA-485 specifications.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Termination Resistor