Rosemount 400A Hydrocarbon Analyzer

The Rosemount 400A, a FID / THC analyzer, is a workhorse! It can measure as low as 1 ppb (part per billion) and as high as 300,000 ppm (parts per million). Its only downfall is a tiny part within the burner itself; it's called the Burner Contact Assembly or also known as "the hotdog." Over the course of years of being lit (and hot), the solder connection between the hot dog's lead wire and the contact barrel breaks down causing a noisy connection and ultimately no signal from the burner.  This analyzer also suffers the same common ailment as any other THC analyzer … contamination. Call us for parts or service.


Typical failures are:

  • Clogged restrictors (makes it hard to light and/or easy to flame-out)
  • Clogged sample capillary (range switch has to be set lower to compensate for less sample being burned)
  • Burner contact assembly ("hot dog") is burned off (noisy display and no response to cal gas)
  • Contamination (zero potentiometer will be very LOW; normal zero pot is > 6.0 turns)
  • Preamp board failed (many symptoms; won’t respond to cal gas or won’t change from high gain to low gain)
  • Thermistor failed (fuel solenoid won’t latch open when ‘purge / ignite’ switch is released)


Not so typical failures include:

  • 90 VDC (polarizing voltage) failure (no response to cal gas)
  • ± 12 VDC failed (display won’t be lit)


Calculator: Click here to download the calculator:  RIGAS 400A calculations.   This is a Microsoft Excel spreadsheet that will help you determine the analyzer’s response to various hydrocarbons.   Please call if you need help getting started/familiarized with this.   

Pictures: 400A_front_view

Parts (recommended): RIGAS 400A parts list

Manual: Rosemount 400A manual rev L

Important factory announcement: As of June, 2020, Rosemount has canceled all new sales of the 400A analyzer. We knew it was coming, and now it's official.  Rosemount intends to support its 400A customer base with parts and service until 2023.  We are inviting you to switch your point of contact for parts and service to us, RIGAS.  We are fully capable of supporting this analyzer now through 2030 ... and possibly beyond that.  We've been servicing this analyzer since our company's founding in 2002; we see about four analyzers per month come through our depot repair facility.  Do you need to see some letters of recommendation or endorsement before you request an RMA? No problem.