This product is no longer available. Some accessories, replacement parts, or services may still be available.
HMP45C-L Temperature and Relative Humidity Probe
Services Available
Repair No
Calibration Yes
Free Support No


The HMP45C is a rugged, accurate temperature and relative humidity probe. It measures relative humidity over the range of 0 to 100% RH and temperature over the range of -40° to +60°C. This probe is suitable for long-term, unattended monitoring, and is compatible with all Campbell Scientific data loggers.

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Benefits and Features

  • Well-suited for long-term, unattended applications
  • Accurate and rugged
  • Mounts to a tripod or tower mast, crossarm, or user-supplied pole
  • 13367 Sensor Head available to facilitate recalibration
  • Compatible with most Campbell Scientific data loggers

This product is available for repair and calibration


Detailed Description

The HMP45C probe uses a HUMICAP capacitive polymer H chip to measure relative humidity and a PRT to measure temperature. Yearly HMP45C recalibrations are recommended.

To reduce the current drain, power can be supplied to the HMP45C only during measurement when the sensor is connected to the data logger’s switched 12 V terminal. Data loggers that do not have a switched 12 V terminal, such as the CR510 or CR7, can use the SW12V switched 12 V device to switch power to the sensor only during measurement.


Supply Voltage 12 Vdc nominal (typically powered by data logger)
Current Drain ≤ 4 mA (active)
Cable Diameter 0.8 cm (0.3 in.)
Sensor Diameter 2.5 cm (1 in.)
Sensor Length 25.4 cm (10 in.)
Weight 0.27 kg (0.6 lb)

Relative Humidity

Sensor Vaisala’s HUMICAP H-chip
Measurement Range 0.8% to 100% RH (non-condensing)
Output Signal Range 0.008 to 1 Vdc
Accuracy at 20°C (against factory reference) ±1% RH
Accuracy at 20°C (field-calibrated against references)
  • ±2% (0% to 90% RH)
  • ±3% (90% to 100% RH)
Temperature Dependence ±0.05% RH/°C
Long-Term Stability Typically, better than 1% RH per year
Response Time 15 s with membrane filter (at 20°C, 90% response)
Settling Time 500 ms


Temperature Sensor 1000 ohm Platinum Resistance Thermometer
Measurement Range -39.2° to +60°C
Output Signal Range 0.008 to 1.0 V
Accuracy at -40°C ±0.5°C
Accuracy at -20°C ±0.4°C
Accuracy at 0°C ±0.3°C
Accuracy at 20°C ±0.2°C
Accuracy at 40°C ±0.3°C
Accuracy at 60°C ±0.4°C


Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.

Data Loggers

Compatible Note
21X (retired)
CR10 (retired)
CR1000 (retired)
CR10X (retired)
CR200X (retired)
CR206X (retired)
CR23X (retired)
CR295X (retired)
CR3000 (retired)
CR3000 (retired)
CR500 (retired)
CR5000 (retired)
CR510 (retired)
CR800 (retired)
CR850 (retired)
CR9000 (retired)
CR9000X (retired)

Additional Compatibility Information


The HMP45C should be housed in a 41003-5 10-plate naturally-aspirated solar radiation shield. The 27251 hex plug is required to mount the HMP45C in the 41003-5. At one time, this hex plug was shipped with the radiation shield but it no longer is. The41003-5 mounts to a tripod or tower mast, crossarm, or user-supplied pole.

FAQs for

Number of FAQs related to HMP45C-L: 1

  1. The HMP60-L (with the Campbell Scientific cable) cannot be used with the 41003-5 10-Plate Radiation Shield without the use of additional hardware. For more information, refer to the Compatibility information on the HMP60-L product page. The standard radiation shield for the HMP60-L is the 41303-5A.