Digital microhmmeter OM 37

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Overview
The AOIP OM 37 is a laboratory and field-capable micro-ohmmeter designed for precise low-resistance measurements. It offers up to 10 A measurement current (pulsed, alternating or continuous) and resolution down to 0.01 μΩ, with an integrated rechargeable battery and a 7-inch colour touchscreen for configuration and readout.

Main applications

• Metallization checks, notably in aeronautics and surface treatments.
• Ground/earth continuity measurements.
• Resistance measurement of motors and transformers.
• Contact resistance testing.
• Electrical and electronic component resistance assessment.
• Cable resistance measurement.
• Mechanical connection and joint tests.

Operation and features
Device configuration and operation are performed via the 7-inch colour touchscreen. User-selectable range, measurement current and mode (pulsed, DC or alternating). Temperature compensation, measurement triggering (manual or automatic) and storage management are available. Built-in rechargeable battery enables measurements at up to 10 A (continuous or pulsed) without external power. Four programmable alarm thresholds with visual and audible signalling and relay outputs are provided.

Power, battery and autonomy
Tabletop instrument powered from mains or from its internal battery pack (5 × Ni-MH D cells, 8.5 Ah). Integrated charger accepts 100–240 V, 50–60 Hz (120 VA). Charging time: 4–6 hours. Battery autonomy: approx. 5000 measurements at 10 A in pulsed mode.

Presentation / Mechanical
Aluminium and galvanised steel enclosure. Dimensions: 380 mm × 310 mm × 130 mm (3U excluding feet). Mass: approx. 7.5 kg (battery included).

Resistance measurement (general)
4-wire measurement with automatic compensation of interference (noise) voltages. Maximum open-circuit terminal voltage: 7 V. Temperature coefficient between 0°C–18°C and 28°C–50°C: ≤ 1/10 of the accuracy per °C.

Ambient temperature measurement for compensation

• Range: 0°C to +50°C
• Resolution: 0.1°C
• Accuracy: ±0.5°C

Resistance measurement — Calibration table (ranges / resolution / 1-year accuracy at 23°C ±5°C / measurement current / voltage drop)
2.50000 mΩ | 0.01 μΩ | 0.01% + 0.3 μΩ | 10 A | 25 mV
5.00000 mΩ | 0.01 μΩ | 0.01% + 0.75 μΩ | 10 A | 50 mV
25.0000 mΩ | 0.1 μΩ | 0.01% + 3 μΩ | 10 A / 1 A | 250 mV / 25 mV
50.0000 mΩ | 0.1 μΩ | 0.01% + 7.5 μΩ | 10 A / 1 A | 500 mV / 50 mV
250.000 mΩ | 1 μΩ | 0.01% + 30 μΩ | 10 A / 1 A / 0.1 A | 2.5 V / 250 mV / 25 mV
500.000 mΩ | 1 μΩ | 0.01% + 75 μΩ | 10 A / 1 A / 0.1 A | 5 V / 500 mV / 50 mV
2.50000 Ω | 10 mΩ | 0.01% + 0.3 mΩ | 1 A / 0.1 A / 10 mA | 2.5 V / 250 mV / 25 mV
5.00000 Ω | 10 mΩ | 0.01% + 0.75 mΩ | 1 A / 0.1 A / 10 mA | 5 V / 500 mV / 50 mV
25.0000 Ω | 0.1 mΩ | 0.01% + 3 mΩ | 0.1 A / 10 mA / 1 mA | 2.5 V / 250 mV / 25 mV
50.0000 Ω | 0.1 mΩ | 0.01% + 7.5 mΩ | 0.1 A / 10 mA / 1 mA | 5 V / 500 mV / 50 mV
250.000 Ω | 1 mΩ | 0.01% + 30 mΩ | 10 mA / 1 mA / 0.1 mA | 2.5 V / 250 mV / 25 mV
500.000 Ω | 1 mΩ | 0.01% + 75 mΩ | 10 mA / 1 mA / 0.1 mA | 5 V / 500 mV / 50 mV
2.50000 kΩ | 10 mΩ | 0.01% + 0.3 Ω | 1 mA / 0.1 mA | 2.5 V / 250 mV / 25 mV
5.00000 kΩ | 10 mΩ | 0.01% + 0.75 Ω | 1 mA / 0.1 mA | 5 V / 500 mV / 50 mV
50.0000 kΩ | 100 mΩ | 0.02% + 7.5 Ω | 0.1 mA / 10 μA | 5 V / 500 mV

Measurement cycle times
Pulsed Mode: ≈ 1 s
Alternating Mode: ≈ 1.5 s
Continuous Mode: ≈ 1 s

Additional features
Types of resistance measured:

• Inductive: coils, transformers, motors, braided cables, etc.
• Non-inductive: metallization checks, ground continuity, contact resistances, flat cables, etc.

Measurement current:

• Internal or external
• DC current from 100 μA to 10 A
• Direct, pulsed or alternating current

Measurement triggering: manual or automatic. Parasitic EMF measurement performed with each measurement. Automatic temperature compensation via external sensor or manual input with programming for metal type or temperature coefficient. Alarms: 4 programmable levels with visual/audible signalling and two relay outputs (1 A / 220 VAC). Outputs: 2 relays.

General specifications (summary)
Dimensions (L × W × H): 380 mm × 310 mm × 130 mm (3U excluding feet). Mass: ≈ 7.5 kg (battery included). Screen: 7-inch colour touchscreen. Power: 115 / 230 V (50 / 60 Hz). Battery with integrated charger: 5 × Ni-MH D, 8.5 Ah; ~5000 measurements at 10 A (pulsed). Communication: USB, Ethernet. Memory: 5000 measurements with average/min/max; on-screen playback and digital/analogue interfaces for data extraction.

Environmental specifications
Reference conditions: 23°C ±1°C (45–75% RH non-condensing). Nominal operating range: 0 to 50°C (20–80% RH non-condensing). Operating limits: -10°C to +50°C (10–80% RH non-condensing). Storage: -30°C to +55°C (-15°C to +50°C with charged battery). Ingress protection: IP40 (EN60529). Maximum altitude: 2500 m.

Technical specifications

• Model: OM 37
• Manufacturer: AOIP
• Measurement method: 4-wire with interference voltage compensation
• Resolution: down to 0.01 μΩ (lowest ranges)
• Measurement current: internal/external DC 100 μA to 10 A; pulsed, continuous or alternating
• Max open-circuit terminal voltage: 7 V
• Screen: 7-inch colour touchscreen
• Battery: 5 × Ni-MH D, 8.5 Ah; integrated charger (100–240 V, 50–60 Hz, 120 VA); charge time 4–6 h; autonomy ≈5000 measurements at 10 A (pulsed)
• Memory: 5000 measurements with average/min/max; playback on screen
• Interfaces: USB, Ethernet
• Alarms: 4 programmable levels with visual/audible signalling and relay outputs (2 relays, 1 A / 220 VAC)
• Dimensions: 380 × 310 × 130 mm (3U excluding feet)
• Mass: ≈ 7.5 kg (battery included)
• Operating temperature: 0 to 50°C (nominal); storage: -30 to +55°C
• Ingress protection: IP40