This product is no longer available and has been replaced by: CR3000. Some accessories, replacement parts, or services may still be available.


The CR21 and CR21L were initially replaced with the 21X and 21XL. Although these loggers have been retired for many years, replacement parts remain available (see Ordering Info).

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:
    CR21 or CR21L Micrologger with
    CR21 Instruction Set (PROMs)
    Alkaline or Rechargeable Power Supply (in base)
    Weatherproof Enclosure (new and old)



  • Seven single-ended analog inputs (-0.2 to +2.5 Vdc or
    -2 mV to +25 mV, FSR)
  • Two pulse count channels (150 Hz (CH 8) and 50 Hz (CH 9), maximum input frequency)
  • One 4 Vac excitation channel
  • Three 2 Vdc sensor excitation channels
  • Two binary inputs
  • Four control outputs
  • One 5 Vdc power terminal
  • One 12 Vdc power terminal
  • One a serial I/O port.