Post Office Box
Product Code : JA-PLE-4258
The Post Office Box (SKU JA-PLE-4258) is a compact Wheatstone bridge with ratio arms, a resistance series and built-in tapping keys, used to measure unknown resistance. The plug-type box has ratio coils of 10, 100 and 1000 ohm and a series of sixteen coils from 1 to 5000 ohm, totalling 11110 ohm, with two silver-contact tapping keys for the battery and galvanometer. This post office box for resistance measurement is offered in constantan and manganin coil versions and in dial type.
Specifications
The plug-type box has three ratio coils of 10, 100 and 1000 ohm and a 1-5000 ohm series (total 11110 ohm), interchangeable brass plugs with oval Bakelite tops, heat-treated and aged coils on Bakelite bobbins, lacquered hard-brass blocks and two silver-contact tapping keys.
| Product | Post Office Box |
| SKU | JA-PLE-4258 |
| Ratio arms | Three ratio coils of 10, 100 and 1000 ohm |
| Resistance series | 16 coils, 1 to 5000 ohm; total 11110 ohm |
| Tapping keys | Two, with silver contacts, for battery and galvanometer |
| Plugs | Interchangeable brass plugs with oval Bakelite tops |
| Coils | Double silk-covered wire on Bakelite bobbins, heat treated and aged |
| Blocks | Corrosion-resistant hard brass, golden lacquered |
| Accuracy (constantan, standard) | 0.05% to 0.1% |
| Constantan versions | Round block; lacquered cabinet-polished; college version with 0.02% to 0.05% accuracy; double-contact heavy blocks |
| Manganin versions | 3 ratio arms, 0.02% to 0.05% accuracy, lacquered, double contacts, in polished teak box; also with heavy gun-metal blocks; 4 ratio arms on request |
| Dial type | One decade per dial on an ebonite base in a polished teak box, with two tapping keys and battery and galvanometer terminals; 5-dial and 6-dial versions |
Applications of the post office box for resistance measurement
The post office box is used as a Wheatstone bridge: the ratio arms are set, the series is adjusted until the galvanometer shows no deflection when the keys are pressed, and the unknown resistance is calculated from the balance values.
- Finding an unknown resistance by the Wheatstone bridge principle
- Determining the specific resistance of the material of a wire
- Checking resistances of coils, resistors and connecting wires
- Class 12 physics practicals and B.Sc electricity laboratories
- Resistance checks in electrical and electronics workshops
Scope of supply and ordering
The listing covers the plug-type post office box in constantan and manganin versions and the dial-type box in 5-dial and 6-dial versions. The version, coil material and ratio arms are confirmed on the quotation, together with accessories, spares and quantities.
Minimum order quantity, lead time and packing are confirmed on each quotation according to the version, quantity and delivery destination. JaincoLab supplies school and college laboratories, bulk education-project orders and export consignments to buyers in Africa, the Middle East and South and South-East Asia.
Frequently asked questions
What resistance values does the post office box have?
Three ratio coils of 10, 100 and 1000 ohm and a series from 1 to 5000 ohm, a total of 11110 ohm.
Which coil materials are available?
Constantan and manganin coil versions are listed, and a dial type with 5 or 6 dials.
What accuracy is available?
Standard constantan boxes are 0.05% to 0.1%; the college constantan and the manganin versions are 0.02% to 0.05%.
Related products
More electricity measurement apparatus is listed in Physics Lab Equipments from JaincoLab, a physics lab equipment manufacturer in India.
Request a quote
To order the Post Office Box, send the version, coil material, quantity and delivery destination through the JaincoLab contact page or email [email protected]. Buying under a laboratory tender? Use our tenders page.
