Formaldehyde Gas Detector (HCHO) RKI FP-31, Riken Keiki


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Formaldehyde Gas Detector FP-31

The FP-31 is a highly sensitive portable gas detector specific for formaldehyde detection. It uses a photoelectric photometry method which utilizes colorimetric tablets for detection. A tablet in placed into the instrument, and then a room air sample is pumped onto the tablet for either a 15 minute or a 30 minute period. If formaldehyde is present, it will cause the chemically impregnated tablet surface to darken or stain. The magnitude of the stain directly correlates to the level of formaldehyde in the air. The stain darkness is read by an optical sensor in the FP-31, and then the instrument calculates the formaldehyde concentration. The FP-31 then has a direct readout of the formaldehyde measurement on an easy to read LCD display. The unit is capable of detecting very low levels of formaldehyde, in order to confirm if an area contains safe breathing levels. There are no known interfering gases, as shown on the chart on the reverse side of this sheet.


Built-in sample draw pump
Photoelectric photometry technology
Direct digital readout
Colorimetric detection tablet method
No false readings from interfering gases
Operates on 4 AA
Stores 99 readings
No warm up time


Furniture and woodworking
Coating and varnishing
Engineered wood products
Medical / veterinary
Painting & corrosion resistant finishes
Carpet manufacture & storage
Heat treatment operations
RV / trailer / mobil home inspecting
Detection Ranges

30 minute sample 0 – 0.4 ppm (0.005 ppm/digit)
15 minute sample 0 – 1.0 ppm (0.01 ppm/digit)

RKI FP-31 Quick Specification

Type Single gas
Target gas Formaldehyde (HCHO)
Detection principle Photoelectric photometry
Power source AA alkaline battery x 4pcs
Continuous operation 12 hours
Dimensions & Weight 80(W) x 150(H) x 40(D) mm, Approx. 250g
Operating temperature & Humidity -10 to 40oC, Below 90%RH

Catalog Formaldehyde (HCHO) RKI FP-31



Riken Keiki

The RIKEN KEIKI (KRI) product lineup includes more than 100 types of gas detectors and environmental monitoring products. Riken Keiki (RKI) Single gas detector range: 
  • 03 Series Smallest Single Gas Monitor
  • GasWatch 3 – Smallest Gas Monitor
  • 04 Series Smallest Toxic Gas Monitor
  • FP-31 Formaldehyde Gas Detector
  • SP-220 Gas Leak Checker for Combustible, Toxic, Freon and Fumigation Gases
  • SC-8000 Portable Toxic Gas Monitor
Riken Keiki (RKI) Multi-gas detector range: 
  • GX-3R Personal Gas Detector
  • GX-3R Pro Gas Detector with Wireless Communication
  • GX-6000 PID Gas Monitor
  • GX-2012 Confined Space Gas Monitor
  • GX-2009 Portable Multi Gas Detector
  • Gas Tracer PPM Leak Detector
  • Eagle 2 Multi Gas Detector for LEL, O2, H2S, CO, VOC & Toxics
  • Eagle Gas Detector
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Detection gas Formaldeyde (HCHO) in air
Detection range 0-0.4 ppm (0.005ppm/digit) 0-1.0 ppm
(0.01 ppm/digit)
Detection time 30 minutes (1,800 sec.) 15 minutes (900 sec.)
Detection principle Photoelectric photometry method
Detection method Colorimetric tablet method (accumulating measurement)
Accuracy ± 20% of reading or ± 5% of full scale (which ever is greater)
Display Digital LCD
Sampling method Sample drawing with built-in pump
Operating conditions -10 ~ 40ºC (14 ~ 104ºF), below 90%RH
Memory Up to 99 readings (automatic recording at the completion of measurement)
Self-diagnosis Failure of light source and light receiver, low battery voltage, pump failure, system trouble
Power Source AA size Alkaline batteries (quantity 4)
Continuous Operation Approximately 12 hours (with no alarm or backlight, with alkaline batteries at 20°C)
Dimension Approx 85(W) x 190(H) x 40(D)mm, 3.35(W) x 7.48(H) x 1.57(W),
Weight 500g, 17.6 oz
Standard Accessories • Detection TAB (20 pcs/pack) ** • AA size alkaline batteries • Operating manual
Optional Accessories Zero and span tab, datalogging software, USB-IRdA cable (for downloading stored data)
Warranty One year material and workmanship


Interference against other gases (typical)
Test Gas Concentration Reading
Toluene 1.0 vol.% 0 ppm
Benzene 1.0 vol.% 0 ppm
Acetoaldehyde 100 ppm 0 ppm
Carbon monoxide 50 ppm 0 ppm
Carbon dioxide 1.0 vol.% 0 ppm
Ammonia 25 ppm 0 ppm
Acetone 1.0 vol.% 0 ppm


Field Test Verification Data
Measurement Place FP-31 DNPH method*
Interior 0.020 ppm 0.025 ppm
Locker 0.030 ppm 0.03 ppm
Furniture 0.040 ppm 0.05 ppm


* Dinitrophenylhydrazine detection method

** Please note: Detection tabs have a six month shelf life. They must be stored in a refrigerator (37°F – 50°F, 3-10°C)

Specifications subject to change without notice.


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