ESYS has expertise with this multi-loop controller.  It has been used in various applications; the one it was designed for is boiler control.  The application that we used it on (and serviced it on) was CEMS (continuous emissions monitoring).

On the CEMS application, the controller handled analog rescaling (for daily automatic re-calibration offsets), solenoid valve control, and some limited threshold/alarm logic.

If you’re looking for a quick fix – try replacing the battery.  That could cure a whole host of problems.

Rosemount 400A is officially obsolete by OEM. No SUPPORT or PARTS from OEM. RIGAS plans to support for the next 10+ years.

As of September 30, 2023, the Rosemount 400A has been officially obsoleted by OEM (Emerson – Rosemount Analytical) with NO OEM PARTS or FACTORY SUPPORT.  There is good news though;  RIGAS plans to support this analyzer for at least the next ten (10) years, and maybe longer.  If you are an end-user, you can help us help you by NOT throwing away good components (boards, regulators, etc.).  Everything is repairable.  Here are a few examples:

  • Main Electronics Board (pre-2009 vintage) – rarely fails. Shipping sometimes causes the big transformer to be ripped off the board
    1. Fixable. We have new transformers.
  • 4-20 mADC card gets noisy or fails outright
    1. Usually a few capacitors dry out causing the “charge pump” to misbehave. We replace the capacitors and fully test the board (includes linearity checks).
  • Backpressure regulator – the rubber diaphragm dries out, becomes brittle, and then it doesn’t regulate pressure very well.
    1. We install a new diaphragm and relap the valve seat; the result is near PERFECT operation (very little seat leakage and great pressure control).
  • Ribbon cables – they get pinched or scraped.
    1. We build our own cables.
  • Sample capillary – it gets clogged over time causing a lack of sensitivity.
    1. It can be cleaned but we’d rather just replace the old capillary (and possibly reuse your old fitting);  capillaries are just soldered into a Parker-Hannifin, tube-end reducer, stainless steel fitting using a Silver bearing solder.
    2. additionally, if your application is unique, we can build a unique capillary.
  • Thermal insulation – it becomes unglued.
    1. We replace the insulation where needed and/or reglue the old insulation.
  • Burner jet gets fouled causing false flame problems or noisy readings.
    1. We make our own jets.
  • Burner contact gets old and brittle, and eventually breaks causing a total loss of analyzer functionality.
    1. We make our own burner contacts (a.k.a., Hot Dogs).

So, in other words, just about everything is repairable.  So, let’s partner up and keep your analyzer running!!!

A side note:  Emerson-Rosemount does NOT have a replacement analyzer for the 400, 400A series.  RIGAS is toying with the idea of building a replacement analyzer and calling it the RIGAS 400R.  It will be VERY similar to the Rosemount 400A but maybe a little easier to operate.  We plan to change the display to read “ppm” rather than percent (%) of scale.  It will also have built in diagnostics for those key parameters that we always ask you about when you call in for technical support.  In the meantime, RIGAS does recommend the Teledyne 4020 THC analyzer (or one of the sister units, like the 4040).


This particular analyzer is one of RIGAS’ favorites to work on (i.e., repair).

Here is a list of some of our checks that we perform before we release your analyzer for shipment:

  1. Noise on range X1 should be minimal (±1 count)
  2. All ranges should be correlated (especially those with an optional range trim board)
  3. Response to certified calibration gas should be equal to or better than factory specifications
  4. When TP5 = 5 VDC then [a] the display reads 100.00, [2] analog output is either 100mV or 1V or 5V (depending on jumper configuration, [3] isolated current output = 20 mADC
  5. Analyzer is clean
  6. Insulation is re-glued
  7. Frayed wires are fixed
  8. Plexiglas is grounded
  9. A/C power switch leads are coated with “liquid electrical tape” to prevent inadvertant electrical shock to the end user
  10. Ribbon cables are pristine
  11. Rear terminal strip has a sticker that shows what functions are on what terminals
  12. Zero pot (potentiometer) is greater than 50% (the higher the number here, the less contamination in the analyzer tubing)
  13. It needs to look good again (paint job if necessary)
  14. Flame safety circuits MUST work properly
  15. Backpressure regulator works as designed (and controls at a very reliable value)
  16. There’s a bunch more, but we don’t want to bore you with the entire list!


Give us a try by calling us at 877-616-0600.