# Digital secondary test-mode indication

Canonical URL: https://eloragrid.ai/symbols/digital-secondary-test-mode-indication
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: DSTI
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: substations
Input: Test or simulation status
Output: Digital test-mode indication

Identifies the selected test or simulation state used by a digital-secondary application.

## In plain English

### What this block does

Identifies the selected test or simulation state used by a digital-secondary application.

### A simple example

In a digital substation bay, a merging unit digitizes local measurements and a protective relay subscribes to the assigned data stream. The command return path and communication-health indications are drawn separately. For this reference, the drawing identifies “Test or simulation status” at the input and “Digital test-mode indication” at the output. Test behavior must match the selected devices.

### What the drawings help you do

Start at the named input: Test or simulation status. Identify its source device or document and the state represented on the drawing. Follow the named output: Digital test-mode indication. Cross-reference its destination and separate the command from confirmation that the equipment responded.

### Terms

- Input: Test or simulation status
- Output: Digital test-mode indication
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: Test or simulation status → DSTI → Digital test-mode indication
A reading guide. The entry's original illustration and input/output facts describe this application.

- [Digital secondary systems: Sampled Values](https://selinc.com/solutions/digital-secondary-systems/sampled-values/)


## What it represents

Identifies the selected test or simulation state used by a digital-secondary application. Digital substation interfaces carry measurements, status and control information between primary equipment and protective devices. Measurement streams, event messages and time synchronization are separate dependencies even when they share an Ethernet network.
In a digital substation bay, a merging unit digitizes local measurements and a protective relay subscribes to the assigned data stream. The command return path and communication-health indications are drawn separately. For this reference, the drawing identifies “Test or simulation status” at the input and “Digital test-mode indication” at the output. Test behavior must match the selected devices.
Identify publisher, subscriber, data meaning and quality handling. Protocol labels alone do not establish protection performance, compatibility or network redundancy; these need the selected system configuration and validation. The functional block is an independent explanation of this named application. Equipment-specific ratings, terminal connections and operating conditions must be established in the project documentation.

## How to read it

- Start at the named input: Test or simulation status. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Digital test-mode indication. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Test behavior must match the selected devices.
- Identify publisher, subscriber, data meaning and quality handling. Protocol labels alone do not establish protection performance, compatibility or network redundancy; these need the selected system configuration and validation.

## Information to show or reference

- Label the source and connection reference for test or simulation status.
- Identify the destination and defined state of digital test-mode indication.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Test behavior must match the selected devices.

## Important distinction

Test behavior must match the selected devices. This reference describes the named application; it does not establish a new IEC graphical symbol, an ANSI device-function number or an exact manufacturer connection diagram.

## Facts

- Representation: Functional block
- Installation focus: Substations
- Input / boundary: Test or simulation status
- Output / connection: Digital test-mode indication
- Lookup label: DSTI is a library lookup label, not a standard device designation.

## Public references

- [Digital secondary systems: Sampled Values](https://selinc.com/solutions/digital-secondary-systems/sampled-values/) — SEL. Public technical context for digital substation process interfaces. Merging units, sampled measurements, GOOSE, process bus and network redundancy. The application text and educational graphic are independently authored; the publisher does not certify this representation.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.