The pen component of a chart recorder is what physically mark the chart paper as data is being recorded. Depending on the variant of traditional recorder that the user possesses, a pen or a heated stylus is required to record data as it is being measured. The pen variant includes an ink cartridge that is attached to a small pen arm with a U-shaped clip. This clip allows it to secure to the chart recorder arm. The stylus variant is metal and screws onto the chart arm connecting point via its own arm. The stylus is thermal-powered and creates indentations on heat-sensitive chart paper. It is attached to the motherboard of the chart recording device via electrical head leads that connect to the stylus arm.
Issues arise when using ink pens due to basic maintenance issues. The pen/s running out of ink halts data measurement and require replacement when this occurs. Pens are also subject to the environment and its level of humidity. Particularly dry climates can dry out chart recorder pens and cause illegible or altogether absent data charts. Pens are easily replaceable no matter their cause of error.
Thermal-stylus pens are different because they are operated by a battery unit. Issues with battery power can prevent the stylus from heating properly, rendering it useless in effective data recording. Manufacturer error can also impact the quality of the thermal stylus and its ability to maintain the appropriate heat in practice. These issues can be solved much like the traditional pen – replace the necessary parts and continue recording.