The CR21 and CR21L were initially replaced with the 21X and 21XL. Although these data loggers have been retired for many years, replacement parts remain available.
Note: The CR21 and CR21L were identical except that the CR21 was powered by alkaline batteries and the CR21L was powered by rechargeable batteries. Within this document, CR21 refers to both models except where specifically stated.
The CR21 featured an integrated design with built-in power supply, keyboard, and display. It looks very similar to, and is often confused with its replacement, the 21X Micrologger. The CR21 stored up to 608 data points in internal memory.
A typical field-based CR21 consisted of the following:
|Single-Ended Analog Inputs||7 (-0.2 to +2.5 Vdc or -2 mV to +25 mV, FSR)|
|Pulse Count Channels||2 (150 Hz [CH 8] and 50 Hz [CH 9], maximum input frequency)|
|4 Vac Excitation Channels||1|
|2 Vdc Sensor Excitation Channels||3|
|5 Vdc Power Terminals||1|
|12 Vdc Power Terminals||1|
|Serial I/O Port||1|