Resistance
The resistance to be measured is connected between terminals TLl and TL2. With the range switch set to the lowest ohms position and the function switch in the Ω position the positive side of the 2.5V stabilized supply is fed to the voltage divider R8/R9. The voltage at the junction of this divider network passes via the rotor and contact 4 of SA11 to one side of the
unknown resistance. The other side of the unknown resistance is connected to Rll via SA9. The voltage developed across Rl1 is fed via the rotor and contact 6 of SC2 to the 40mV point (junction of R114 and R115) along the main chain of series resistors and thence to the amplifier as in the d.c. mode (see para. 4.3.1.(i)).
On the higher resistance ranges the potential divider R8/R9 is made inoperative since switch
SAl is open but R9 forms part of a series network with Rl to R6. R1-R6 ,corrected slightly by R11-R14 and the input resistance of the amplifier, are chosen so that ,with the terminals short circuited, the meter reads full scale, i.e. zero ohms.
It follows that these resistors are equal to the half-scale mark on their respective ohms ranges. The voltage across R11-R14 is fed to the 40mV point as for the low ohms range; on the MΩ x 1 0 range no additional shunt is necessary,the amplifier input resistance itself being used for the purpose.