Gain is selected with a jumper connection (see Figure 7-1). With no jumper installed, G = 10 V/V. With a jumper installed, G = 100 V/V. To preserve good gain accuracy, this jumper must have low series resistance. A resistance of 0.5 Ω in series with the jumper decreases the gain by 0.1%.

Internal resistor ratios are laser trimmed to provide excellent gain accuracy. Actual resistor values can vary by approximately ±25% from the nominal values shown.

Gains between 10 V/V and 100 V/V are achieved by connecting an external resistor to the jumper pins. However, this configuration is not recommended because the ±25% variation of internal resistor values makes the required external resistor value uncertain. A companion model, the INA128, features accurately trimmed internal resistors so that gains from 1 V/V to 10,000 V/V can be set with an external resistor.