Ex i Entity Parameter Validator

Validate an intrinsically safe (Ex i) loop in seconds. Enter transmitter, barrier, and cable parameters; the tool checks all five IEC 60079-11 inequalities and flags any that fail, with an optional 30% NEPSI commissioning margin.

Transmitter side (from datasheet)

Barrier / galvanic isolator (safe-area side)

Field cable (loop run)

Try a preset

Click Validate Loop to check the five entity-parameter inequalities for this combination.
30% NEPSI margin (default ON): Chinese metallurgy and petrochemical commissioning practice holds 30% headroom on the Co − Ci and Lo − Li calculations for cable runs over 200 m, because temperature drift across an Asian summer can shift cable capacitance by up to 10%. Toggle off if you want only the bare IEC 60079-11 inequality check.

Common Ex i Pairings: Quick Reference Table

Pairing Uo / Io / Po Co / Lo Tx Ci / Li Cable headroom
HMK HM60 + Pepperl-Fuchs KFD2-STR Zener barrier25.2 V / 93 mA / 587 mW107 nF / 3300 μH20 nF / 100 μH435 m at 200 pF/m (with 30% margin: 312 m)
HMK HM50 + Phoenix Contact MACX MCR-EX-SL galvanic isolator24 V / 100 mA / 600 mW160 nF / 5000 μH15 nF / 50 μH906 m at 160 pF/m (with 30% margin: 689 m)
HMK HM28 + STAHL 9165 isolator25.2 V / 93 mA / 600 mW107 nF / 3300 μH5 nF / 10 μH510 m at 200 pF/m (with 30% margin: 379 m)
HMK HE60 OEM + KFD2-STR Zener barrier25.2 V / 93 mA / 587 mW107 nF / 3300 μH8 nF / 25 μH495 m at 200 pF/m (with 30% margin: 366 m)
Reference values; verify against the latest datasheet of each component before commissioning.

How to Use This Validator

  1. Read the transmitter datasheet for the five Ex i entity parameters under “Intrinsic Safety Marking”: Ui, Ii, Pi, Ci, Li. These are the device’s safety ceilings.
  2. Read the barrier or galvanic isolator datasheet for Uo, Io, Po, Co, Lo on the field-side terminal pair. Use the entity-parameter table for the specific output channel you are wiring.
  3. Look up the cable spec. Typical instrumentation cable runs 150 to 250 pF per metre for capacitance and 0.7 to 1.2 μH per metre for inductance. Use the actual cable run length in metres, end-to-end.
  4. Click Validate Loop. The tool reports five PASS / FAIL checks. All five must pass for the loop to qualify as Ex i certified in that configuration.
  5. Apply the 30% NEPSI margin for cable runs over 200 m, outdoor installations exposed to seasonal temperature swings, or any commissioning that will be filed with NEPSI / EAC / IECEx audit teams. Toggle the margin off only for the bare IEC 60079-11 baseline check.

The Five Entity-Parameter Inequalities

An Ex i loop is certified only when all five inequalities below hold simultaneously, with the barrier at the safe-area side and the transmitter at the field side:

  • 1.   Uo ≤ Ui   — barrier output voltage cannot exceed transmitter input rating
  • 2.   Io ≤ Ii   — barrier output current cannot exceed transmitter input current rating
  • 3.   Po ≤ Pi   — barrier output power cannot exceed transmitter input power rating
  • 4.   Co ≥ Ci + (Ccab/m × Length)   — barrier max external capacitance must absorb device + cable storage
  • 5.   Lo ≥ Li + (Lcab/m × Length)   — barrier max external inductance must absorb device + cable storage

The first three inequalities cap the total energy that can reach the field side under fault. The last two ensure the energy stored in cable + device reactive elements cannot, during a discharge transient, exceed the gas-group ignition threshold for the rated zone.

The optional 30% NEPSI commissioning margin raises inequalities 4 and 5 to 1.3 × (Ci + Ccable) and 1.3 × (Li + Lcable). This is standard practice in commissioning reports filed to NEPSI in China and increasingly referenced by Indian and Vietnamese audit teams reviewing imported instrumentation, because cable capacitance can drift up to 10% across an Asian summer temperature swing.

More HMK engineering tools to use alongside this validator:

HMK HM60 Ex i / Ex d sapphire pressure transmitter

HMK HM60 Sapphire Pressure Transmitter

Dual-certified Ex d IIC T6 Ga and Ex ia IIC T6 Ga; -100 kPa to 100 MPa range; 4-20 mA passive with HART 7.

HMK HM50 anti-corrosive Ex i pressure transmitter

HMK HM50 Anti-Corrosive Pressure Transmitter

Hastelloy C-276 and PTFE wetted parts; Ex i certified for chemical and acid service in Zone 0/1/2.

HMK HE60 OEM Ex i pressure sensor

HMK HE60 OEM Pressure Sensor

OEM-class form factor with Ex i certification; ideal where a compact intrinsic-safety variant is required.

Frequently Asked Questions

Entity parameters are the five values printed on every Ex i certificate: Ui, Ii, Pi, Ci, Li for the field device and Uo, Io, Po, Co, Lo for the safe-area barrier. They quantify the maximum voltage, current, power, capacitance, and inductance the device can safely accept (or supply, for the barrier). When all five inequalities hold, the loop cannot release enough energy to ignite the worst-case gas mixture in the rated zone.

Field cable adds distributed capacitance and inductance to the loop. Even a short run of 100 m at 200 pF per metre adds 20 nF on top of the device’s internal Ci. If Ci + Ccable exceeds the barrier’s maximum allowed Co, the certified configuration is broken even though every individual datasheet looks fine. This is the most common cause of failed audits.

Chinese metallurgy and petrochemical commissioning practice holds 30% headroom on the Co minus Ci and Lo minus Li calculations for cable runs over 200 m, because temperature drift across an Asian summer can shift cable capacitance by up to 10%. The margin is standard in NEPSI-supervised commissioning reports and increasingly referenced by Indian and Vietnamese audit teams. The validator applies it by default; toggle off for the bare IEC 60079-11 check.

Their entity parameters differ. Zener barriers are passive, single-channel, and reference plant earth, with typical Uo around 25 V. Galvanic isolators are active, transformer-coupled, and have no earth dependency; their Uo can be lower (around 24 V) and their Co / Lo headroom often higher. Always check both datasheets — never assume one substitutes for the other on a given certified loop.

Po ≤ Pi caps the steady-state power that can reach the field side. Without this cap, a fault on the safe-area side could push enough current through a short circuit to overheat a device wire or PCB trace to ignition temperature, even if the voltage and current limits individually are met. Po is the integrated worst-case fault energy.

No. The five inequalities together define the certified configuration; failing any one of them voids the certificate for all rated zones, including Zone 2. You can re-spec by either choosing a different barrier (one with higher Co or Lo), shortening the cable run, or moving to a transmitter with lower Ci or Li. The HMK HM28 and HE60 both have lower internal storage than typical industrial transmitters and are useful when cable headroom is tight.

Need to Spec an Ex i Pressure Loop for Your Plant?

If your validator output flags any inequality as failed and you are not sure which side to change — barrier, cable, or transmitter — send the spec to the HMK pressure engineering team. We work through the entity-parameter math with you and recommend a configuration that passes both IEC 60079-11 and NEPSI commissioning checks.

Our engineers typically respond within 12 business hours with a complete entity-parameter analysis and product recommendation.

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