Loop power budget para sa 4-20 mA loops
Tingnan ang voltage na naiiwan ng 4–20 mA loop sa transmitter.
Reads AS/NZS 3008.1.2:2017 (NZ) and AS/NZS 3008.1.1:2017 and 2025 (AU). Tables checked 27 Sept 2026.
Subukan ang isang job 6
Nilalagyan ng halimbawang value ang bawat job. Palitan ang mga ito ng sarili mong value.
- Check a 4–20 mA loop's power budgetThe supply, the series resistance and the cable give the voltage left at the transmitter.
- Check a loop with a HART resistorThe voltage left with a 250 Ω HART resistor in the loop.
- Check a loop through a barrierThe voltage left with 300 Ω of barrier in series.
- Check a 2 km loopThe voltage left on 1 mm² cable over 2000 m.
- Check a loop on a 12 V supplyWhether a 12 V supply drives the loop.
- Check a loop at fault currentThe voltage left at 22 mA.
Mga input
Worked example gamit ang mga default na input.
- Loop supply voltage
- 24 V
- Pinakamababang boltahe ng transmitter
- 12 V
- Loop current
- 20 mA
- Input resistance
- 250 Ω
- HART resistor
- 0 Ω
- Ibang series resistance
- 0 Ω
- Haba ng cable, isang direksyon
- 500 m
- Resistance ng conductor
- Mula sa laki ng conductor
- Laki ng conductor
- 1 mm²
- Standard
- NZ · AS/NZS 3008.1.2
Voltage margin
6.48V
- Voltage sa transmitter
- 18.48V
- Loop resistance
- 275.8Ω
- Resistance ng cable
- 25.8Ω
- Pinakamataas na loop resistance
- 600Ω
- Pinakamahabang cable
- 6,782m
Design aid lang ang resultang ito. I-verify ito laban sa kasalukuyang standard.
Mga hakbang ng kalkulasyon
- Resistance ng conductor25.8Ω/km
AS/NZS 3008.1.2:2017 Tables 34 to 35
- Resistance ng cable, parehong konduktor25.8Ω
- Resistance sa series250Ω
- Loop resistance275.8Ω
- Loop current20mA
- Voltage drop sa loop5.52V
- Boltahe sa transmitter18.48V
- Voltage marginResulta6.48V
- Pinakamataas na loop resistance600Ω
- Pinakamahabang haba ng cable6,782m
Tungkol sa calculator na ito
How the tool checks the loop
A 4–20 mA loop is one series circuit. The loop supply drives the current through the transmitter, the cable and the receiver input. The transmitter needs a minimum voltage at its terminals to work.
- Conductor resistance. The tool reads the resistance of a copper conductor for the size you pick. It can also take the value from the cable data.
- Cable resistance. The current goes out on one conductor and comes back on the other. So the tool doubles the one-way length.
- Loop resistance. It adds the cable resistance to the input resistance, the HART resistor and any other series parts.
- Voltage at the transmitter. It multiplies the loop current by the loop resistance and subtracts that drop from the supply voltage.
- Voltage margin. It subtracts the transmitter minimum voltage. A margin of 0 V or more passes.
- Maximum length. It gives the longest one-way run that keeps the margin at 0 V or more.
Worked loops
Each line opens the tool with its values. Every line uses a 24 V supply, a 12 V transmitter minimum voltage and a 250 Ω receiver input.
- Pressure transmitter, 500 m of 1 mm² at 20 mA. The loop passes with a margin of 6.48 V.
- HART loop, 400 m of 1 mm² at 22 mA. A 250 Ω HART resistor sits in the loop. The loop passes with a margin of 0.55 V.
- HART loop, 500 m of a 36 Ω/km pair at 22 mA. The resistance comes from the cable data. The loop passes with a margin of 0.21 V.
- The same HART loop at 700 m. The loop fails with a margin of −0.11 V. Shorten the run, use a larger conductor or raise the supply.
New Zealand and Australia
The Standard select picks the part of AS/NZS 3008.1 the tool reads for the conductor resistance. Part 1.2 is the New Zealand part, 2017 edition. Part 1.1 is the Australian part. For Australia, the Edition select picks 2025 or the superseded 2017 edition. All three print the same resistance values. The impedance table entry says how AmpSize checked them.
Related checks
- The comms cable selector checks the cable construction and the run length for the interface.
- The DC cable size calculator sizes the 24 V d.c. supply cable to the transmitter panel.
- The segregation checker checks the spacing between the loop cable and power cables.
Mga tanong
Design aid ang resulta. I-verify ito laban sa kasalukuyang standard.
Ano ang nagtatakda kung gaano kalayo ang maaaring i-run ng 4–20 mA loop?
Ang supply voltage, na binawasan ng minimum voltage ng transmitter, ang budget. Ginagastos ito ng loop current na dumadaan sa bawat series resistance. Dinadagdagan ng cable ang resistance ng dalawang conductor, kaya mas malaking gastos ang mas mahabang run o mas manipis na conductor.
Bakit magche-check sa higit sa 20 mA?
Puwedeng magpadala ang transmitter ng higit sa 20 mA, halimbawa ang upscale alarm na malapit sa 22 mA. Tumataas ang drop sa loop habang tumataas ang current. Tingnan sa pinakamataas na current na kayang ipadala ng transmitter.
Saan ko makikita ang minimum voltage ng transmitter?
Ibinibigay ito ng data sheet ng transmitter, kadalasan bilang lift-off voltage o minimum terminal voltage. May ilang data sheet na nagbibigay ng load line sa halip. Basahin ang voltage sa pinakamataas na loop current.
Background
Mga clause at table na binabasa ng tool na ito
- AS/NZS 3008.1.2:2017 Table 30, 34, 35Reactance at 50 Hz and a.c. resistance at 50 Hz
- AS/NZS 3008.1.1:2017 Table 30, 34, 35Reactance at 50 Hz and a.c. resistance at 50 Hz
- AS/NZS 3008.1.1:2025 Table 4.1(A), 4.1(B), 4.5(A), 4.5(B)Reactance at 50 Hz and a.c. resistance at 50 Hz
Bawat clause at table, kasama kung paano ito na-verify
Huling na-check ang mga table noong 27 Sept 2026.
Mga kaugnay na tool
Nakatulong ba ito?
May tanong, o may value na mukhang mali? Makipag-ugnayan sa amin.