What should the input impedance of a DMM be when testing computer-controlled systems?

The input impedance of 10 megohms is critical when testing computer-controlled systems because it minimizes the loading effect on the circuit being measured. In electronic measurement, a high input impedance allows the digital multimeter (DMM) to draw very little current from the circuit. This is particularly important in sensitive electronic systems, such as those found in computers and automotive applications, where even small amounts of current drawn by a measuring device can alter the performance or behavior of the system being tested.

Using a DMM with a high input impedance (like 10 megohms) ensures that the measurements reflect the true conditions of the circuit without significantly affecting the circuit's operation. This contrasts with lower impedance options, which might significantly influence the circuit, leading to inaccurate readings. For example, an input impedance of 1k ohms or 10k ohms can overload certain signals, especially in low-current or high-impedance circuits. Thus, selecting a DMM with an input impedance of 10 megohms is ideal for preserving the integrity of the measurements in computer-controlled systems.