The post was last updated on 2022-02-28.
Besides a reference and a redox electrode, a device to store the data including a voltmeter and a multiplexer (for multiple readings with multiple redox electrodes) are needed. I consider the data logger therefore as a single unit in the measurement routine. The multiplexer should be equipped with a very high impedance for all individual redox channels > 1013 Ω (= 10 Teraohm; TΩ). This is mandatory in order to obtain a stable reading. Data logger can sometimes be equipped with a modem and the data can be transferred to a webserver via General Packet Radio Service (GPRS), as shown in the example below:
For most applications, a measuring interval every hour is recommended to relate the EH to environmental boundary conditions (which can fluctuate significantly on a short temporal scale) and collect data over years to centuries to derive long term trends. Thereby, even though a lot of data is gathered, you do not get lost within your data, e.g., collected on a minute interval.