Description
Vista Scientific 7840 Psychrometer Humidity Meter w/ Thermometers For Parts
The Vista Scientific 7840 is a sling-style psychrometer used for measuring relative humidity and dew point by reading the temperature difference between a wet-bulb and dry-bulb thermometer pair. This unit is being sold as-is for parts or salvage only. It has significant internal corrosion resulting from leaking battery acid, which the seller considers non-repairable. One plastic end cap has a chip missing. The two glass thermometers are included and appear intact.
Specifications & What's Included
- Brand: Vista Scientific Corporation
- Model: 7840
- Type: Psychrometer (wet-bulb / dry-bulb humidity instrument)
- Housing length: approximately 12 inches
- Thermometer length: 10 inches each
- Includes: two glass thermometers (wet and dry bulb)
- Adjustment knob present on housing (visible in photos)
- Printed temperature/humidity scale on housing
- Brown plastic end caps (one has chipped plastic)
- Internal condition: significant rust corrosion from battery acid leakage — non-repairable per seller
- Sold strictly as-is for parts, repair, or salvage
Applications
Psychrometers of this type are used to measure relative humidity by recording the readings of two thermometers — one with a wetted wick (wet bulb) and one exposed to ambient air (dry bulb). The difference between the two readings, read against a chart or scale on the instrument, yields relative humidity and dew point. The Vista Scientific 7840 was designed for laboratory, HVAC, greenhouse, and general environmental monitoring applications where accurate humidity readings are needed without electronic sensors. These instruments date from an era — roughly the 1970s through 1990s — when analog wet-dry bulb psychrometers were standard humidity tools in labs and industrial facilities before digital hygrometers became dominant. Parts-only units like this may be useful for thermometer salvage, educational display, or restoration projects.
This Vista Scientific 7840 Psychrometer is being sold as-is for parts or repair. The unit has significant internal corrosion caused by leaking battery acid, which the seller considers non-repairable. One end cap has a chip of plastic missing, visible in the photos. The two glass thermometers (10 inches in length) are included and appear intact. The housing measures approximately 12 inches in length. This item is not guaranteed functional and is offered strictly for parts, salvage, or display purposes. Please view our photo set and contact us if you have any questions.
Warranty Information
Additional Information
Brand: |
Vista Scientific |
Model: |
7840 |
MPN: |
7840 |
Type: |
Psychrometer |
SKU: |
9663 |
Condition: |
As-Is / For Parts or Not Working |
Seller Notes: |
Includes two 10-inch glass thermometers. Housing is 12 inches. Sold as-is for parts. |
Country/Region of Manufacture: |
United States |
Form Factor: |
Handheld / Portable |
Measurement Type: |
Relative Humidity / Wet-Dry Bulb Temperature |
Thermometer Length: |
10 inches |
Housing Length: |
12 inches |
Application / Use Case: |
Humidity and dew point measurement, HVAC, meteorology |
Included Components: |
Two glass thermometers (wet and dry bulb) |
Condition Notes: |
Vista Scientific 7840 Psychrometer sold as-is for parts. Internal rust from leaking battery acid — considered non-repairable. End cap has chip of plastic missing. Two 10-inch thermometers included. Not functional, no guarantee. |
