Lab Bridges

a) Callendar & Griffiths Bridge Senior :-

MERCURY Contact for precision work and Temp- is measureable to 1/100th C . The resistance coils are of MANGANIN and arranged according to BINARY scale and can be checked on the BRIDGE itself. FINE slow motion is provided by a lever & can be read by vernier attached. The coils are married in units 10, 20, 40, 80, 100, 320, 640 & 1280. Terminals provided for “PL”, “CL” Galv & Battery, Mercury cups filled half with mercury and “U” connectors serve to short the resistance when depressed in Mercury. Instruction sheet provided for guidance without meroury.

b) Callender and Griffiths Bridge :-

It is an improvement over the potentiometer. The 50cm long slides wire of 1 ohm resistance is calibrated into 100 equal parts. 14 coils are arranged in series in dial from each being of 1 ohm resistance.

c) High Resistance by Leakage of condenser Method :-

Comprising a wooden Board for proper setting of Components & Special CHARGE & DISCHARGE key fitted with restless points & a set of terminals for Ballistic Galv condenser and Plug key in series with 20-M-OHM resistance. Two way key is provided for charging the condenser and discharging through resistance coil after known interval. Tap Key Provided on the panel for use of Ballistic Galv.

a) General :

This bridge is fully portable with a built in sensitive Galvanometer and a dry battery. The bridge is extremely useful for resistance measurements with a fair degree of precision.

b) Series Arm :

There are 4 decades of 10 x 1, 10 x 10, 10 x 100 and 10 x 1000 ohms.

c) Range Multiplier :

A single rotary switch furnishes 7 range multipliers of x 1000, x100, x10, x1, x0.1, 0.01 and 0.001.

d) Range of Measurement :

0.01 Ohm to 1.11 mega ohms.

e) Battery :

A dry battery of 4.5 volts is built-in provision is there for using external battery for measuring high resistances.

f) Galvanometer :

The bridge can be supplied with types of built-in galvanometer.
1) Student galvanometer of M.O. 65 model, and of sensitivity 10 microamperes/mm.
2) Taut suspension galvanometer of coil resistance 100 ohmsand sensitivity of 0-5 microampere per mm and with a mechanical coil locking device and a zero adjuster.
3) In both models, external more sensitive galvanometer such as our spot reflecting galvanometer as above can be use for greater discrimination and accurate null point.

g) Resistance Coil :

Manganin coil which are non inductivity wound, aged and properly varnished are used.

h) Push Button :

Two push buttons for battery and galvanometer are provided.

i) Accuracy :

Both series and ratio coils are adjusted to an accuracy of better than 0.05%
1) Overall Accuracy of measurements is better than + 0.1%
2) With Students galvanometer of M.O. 65 model
3) With Taut suspension galvanometer.

a) Multiplying Ratio :-

A rotary switch furnishes 5 multiplying ratios of x 100, x10, x1, x0.1 and x0.01.

b) Range of Measurement :-

The bridge had a range of 0.2 micro ohm to 11 ohms.

c) Maximum Current :-

10 amperes intermittently and 5 amperes continuously.

d) Resistance Coils :-

Manganin coils are used.

e) Terminal :-

Terminals for battery, galvanometer current and potential terminals are all provided on the backelite panel enclosed in a teak wood box.

f) Current Reversing Switch :

A battery reversing switch is provided to reverse the current in the bridge to eliminate thermal effects.

g) Accuracy :-

0.5% + 1 small division of the slide wire.

h) Industrial Kelvin Double Bridge :-

The above bridge can be supplied with an additional range factor of x 1000 to give the range of measurement as 0.2 micro ohms to 110 ohms at extra cost.

i) Adjustable Heavy Duty D.C. Current source :-

It is a useful and economical substitute for a D.C. battery. The unit is mains operated and can deliver a continuously adjustable D.C. current of 0 to 10 amperes maximum.
The unit consists of a variac, a step down transformer. A bridge rectifier, filter circuit and an ammeter of 0 to 10 amperes to read current.

Input Voltage :-

230 volts A.C. Mains at 50C/s.

D.C. Output :

Approximately 0 to 10 volts continuously adjustable to give a variable current of 0 to 10 amperes depending upon external lead.

j) Conductivity Attachment:-

It is an arrangement to hold specimens in the form of wires, rods, strips etc. Separate current and potential terminals are provided. Distance between potential points is 500 mms it can hold specimens of any size between ½” dia rod to 42 S.W.G. wires.

k) Potentiometer Shunts :-

These are precision shunts suitable for calibration of Ammeters etc. with the help of D.C. Potentiometer. These shunts are provided with 4 terminals (current and potential), They can be supplied with standard milli volt drop of 75 milli volts.
Resistance in ohms 
a) 0.005 b) 0.0025 c) 0.001 d) 0.005

a) Portable Wheatstone Bridge (Modified)

This bridge is exactly except of additional facility of murray and varley loop tests for location of faults in cables. The bridge is suitable for resistance measurements also.

b) For resistance measurements and varley loop test.

There are 7 Multiplying factors of x 1000,x100 x10, x 1, x.01 and .001.

c) For murray loop tests

3 additional multiplying factors of 10 M, 100 M and 1000 M are provided.

d) Special switching arrangement has been provided to carry out conductance tests, varley loop test and murray loop test.

e) Rest of the feature like series arm, battery galvanometer, push buttons system are same as above.

f) Same as above but with Constanta coil. 
1) With MO 65 Galvanometer.
2) With taut suspension Galvanometer.

a) Kohirausch Conductivity Bridge :-

For direct measurement of electrolytic resistance or thick values of D.C resistance. Slide wire enclosed calibrated to read 01 to 10on Circular Scale. In conjunction with multiplier knob giving 6 ratio 0.1, 1, 10, 100, 1000, 10,000 are obtainable so that total Range of measurement. 001 to 100000 ohms Robust push-button key that can be locked is provided.

b) Kohirausch Conductivity Bridge :-

Comprising of calibrated scale 0.1 -10 ohm,s and multiplier ratio dial giving 6 ratio dial giving 6 ratio 0.1, 1, 10, 100, 1000, 10,000 Maganian slide wire is used. Push button key of robust type is useful for quick determination of resistance too, when galvanometer replaces the head Phone in the detector circuit, with constant coil Accuracy 1%

c) Same as above but of routing quality.

d) Thermo-EMF Temperature Bridge :-

Direct reading, specially designed for thermocouple measurements. Comprising 20 coils worked by a knob marked x0.5 M/V in series with in slide wire 50 cm divided into 500 mm. Calibrated to read 0.5M/V giving a Potential gradient 1 Micro volt per mm. Total measurable EMF is 10.5 m/volt. Rotary switch provided for SELECTOR Switch for 2 External circuits on being Thermo Couple. External standardizing coil for Weston Normal cell provided.

e) Induction Coil :-

To be used with kohirausch conductivity Bridge.

f) Head Phone :-

Extra sensitive for use with kohirausch Conductivity Bridge.

a) Standard Resistance :-

10 coils of 0.1 ohm each are arranged on a rotary dial and a circular slidwire of total resistance 0.1 ohm and of 100 division is in series with the 10 coils. Each division of the slide wire is equal to 0.001 ohm on the normal range.

1) Multiplying Ratio :-
A single rotary switch furnishes 3 multiplying ratios of x1, x0.1 and x0.01
2) Range of Measurement :- 
1.1 to 0.00001 ohms on different ranges.
3) Maximum Current :- 2 amperes
4) Panel :- A backlite panel enclosed in a teak wood box is used, Separate current and potential terminals, battery and galvanometer terminals, push buttons for battery and galvanometer are provided on the panel.
5) Accuracy :- + 0.1%
6) Coils :- Manganin Coils are used

b) Kelvin Double Bridge :-

Standard Resistance in steps of 0.01 ohm in series with a calibratedslidewirs 100 divisions equal to 0.01, ohms Rotary type multiplier switch 0.01, 0.1, 1, 10 and 100 gives a range of measurement 0.000001 to 1.1 ohm.

c) Conductivity attachment :-

It is an arrangement to hold Specimens in the form of wires rods, strips etc. Distance between potential points is 500 mms, sparate current and potential terminals are provided.

d) Industrial Kelvin Double Bridge:Standard resistance :

There are 10 coils of 0.01 ohm each arranged on rotary dial plus a circular slidewire of total resistance 0.01 ohm and 500 sub divisions. Each sub-divison is equal to 0.00002 ohms on the normal range.