Post Office Box-Plug Type (Constantan and Manganin Coil) Manufacturer,Supplier and Exporter in India
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Product Code : EL-PLE-10278
Lab Instruments Manufacturers manufactures the Post Office Box – Plug Type (Constantan and Manganin Coil) in-house at our own India facility, supplying it to physics laboratories in schools and colleges, and as an OEM/private-label item to distributors and exporters across India and internationally.
What This Instrument Does
This Post Office Box is a plug-type resistance box built on the Wheatstone bridge principle, used to accurately measure an unknown resistance between 0.1 and 1,111,000 ohms using a DC battery. The 3-Ratio version has sixteen non-inductively wound coils (1, 2, 2, 5, 10, 20, 20, 50, 100, 200, 200, 500, 1000, 2000, 2000, and 5000 ohms) plus two proportional arms, each with coils of 10, 100, and 1000 ohms. The 4-Ratio version has the same sixteen coils, plus two proportional arms each with coils of 1, 10, 100, and 1000 ohms, and additionally incorporates an infinity gap. Two spring keys with good contact are provided for the battery and galvanometer connections, and the whole system is housed in a superior-quality wood box.
Constantan or Manganin Coil, 3-Ratio or 4-Ratio
This Post Office Box is available in both 3-Ratio and 4-Ratio configurations, and with either constantan or manganin resistance coils. Both coil types use a 12mm and 14mm thick rectangular brass block. The constantan-coil version is accurate to within ±0.1%, while the manganin-coil version is accurate to within ±0.05%.
| Specification | Detail |
|---|---|
| Measurable resistance | 0.1 to 1,111,000 ohms, using a DC battery |
| 3-Ratio coils | 16 coils (1, 2, 2, 5, 10, 20, 20, 50, 100, 200, 200, 500, 1000, 2000, 2000, 5000 ?) + 2 proportional arms (10, 100, 1000 ? each) |
| 4-Ratio coils | Same 16 coils + 2 proportional arms (1, 10, 100, 1000 ? each) + infinity gap |
| Connections | 2 spring keys for battery and galvanometer |
| Coil material options | Constantan (±0.1% accuracy) or Manganin (±0.05% accuracy), 12mm & 14mm thick rectangular brass block |
| Housing | Superior-quality wood box |
Typical Use
College and university physics laboratories use this Post Office Box for precision resistance-measurement experiments based on the Wheatstone bridge method, where the coil material and ratio configuration are chosen to match the required accuracy.
Manufactured In-House
This instrument is manufactured at our own India production facility. Manufacturing in-house means our team controls coil winding and brass block accuracy at every stage, and can produce custom configurations or bulk sets for a specific institutional order or export shipment without waiting on an outside supplier.
Frequently Asked Questions
What resistance range can this Post Office Box measure?
Between 0.1 and 1,111,000 ohms, measured accurately using a DC battery.
What is the difference between the constantan and manganin coil versions?
Both use a 12mm and 14mm thick rectangular brass block; the constantan-coil version is accurate to within ±0.1%, while the manganin-coil version is accurate to within ±0.05%.
What is the difference between the 3-Ratio and 4-Ratio versions?
Both share the same sixteen main coils; the 4-Ratio version adds proportional arms of 1, 10, 100, and 1000 ohms plus an infinity gap, compared to the 3-Ratio version's 10, 100, and 1000 ohm proportional arms.
Related Equipment
Bridge experiments also call for the Potentiometer, 1m Single Wire and the Pencil Jockey, while the Resistance Box and the Resistance Box, Decade Dial Type supply known resistances. Browse Physics Lab Equipments in Physics Lab Equipment, or send tender details via Tenders.
Last updated: October 2026.
