Measurement of High Impedance Materials

For measurement of high impedance materials, 2-terminal test connections to the sample are usually used. This is because the impedance of the sample is generally much greater than the impedance of the test cables therefore, any errors introduced by the cables are unlikely to significantly affect the sample measurement results. This is true at low frequency in particular but at high frequency, specialist techniques are often needed to minimize errors due to cables and these will be discussed later in this section. 

It is important in many applications to have very sensitive current measurement capability for measurements at low frequency (less than 1 Hz) where the impedance of a wide range of materials becomes very high. This is especially fine for ceramic and other insulator materials. 

---

Most modem potentiostats provide at least four connections to the cell. These connections typically consist of a counter electrode (CE) that provides current to the ceU, a working electrode (WE) that provides measurement of the current through the cell, and at least two reference electrode inputs (RE) for voltage measurement. Potentiostats that have 4-terminal connections are capable of 2, 3 or 4-terminal testing of electrochemical cells (Figure 3.2.2). The 2-terminal test technique is used mainly for the measurement of high impedance materials where the impedance of cables is not significant (see Section 3.2.2.3). 

---