Analog Loop Health

Loop voltage drop, remaining headroom, and how the installed resistance compares with Rmax at 20 mA (INST-10).

Instrumentation & ControlsElectrical & Power

Loop voltage drop, remaining headroom, and how the installed resistance compares with Rmax at 20 mA (INST-10).

App id: INST-40. Reference version 1.0.

How to fill it

Fill the inputs. The tool shows the outputs.

On the tool screen, Calc is the working sheet. Presets stores values you reuse. Reference is the formula, assumptions, and provenance below.

Formula

V_drop = I R;  remaining = V_supply − V_drop;  Rmax = (V_supply − V_tx,min) / 20 mA

Inputs

Name	Unit
Supply voltage	`V`
Loop current (camera)	`mA`
Loop resistance	`ohm`
Transmitter minimum	`V`
Expected current (optional)	`mA`

Outputs

Name	Unit
Remaining voltage (hero result)	`V`
Voltage drop	`V`
Maximum loop resistance	`ohm`
R / Rmax	`%`
Current vs expected	`mA`

Diagnose

Observations are context. They do not pass or fail a structure. See Diagnose.

When	Observation	Severity
`loop current < 3.6 mA`	Below 3.6 mA	warning
`loop current < live zero`	Below live zero	caution
`loop current > 21 mA`	Above 21 mA	warning
`loop current > live full`	Above live full scale	caution
`loop current ≤ live full`	In measurement range	info
`Remaining voltage < Transmitter minimum`	Insufficient transmitter headroom	warning
`Remaining voltage < Transmitter minimum + 2`	Thin voltage margin	caution

Assumptions

Rmax is evaluated at 20 mA. Enter expected current to see signal error; otherwise that output is omitted.

Provenance

Composes INST-09 drop and INST-10 Rmax. Not a cable-fault locator.