RIGAS 400A normal repair activities

This is a short list of activities that we perform on your analyzer:

  • First, we do AS-FOUND testing
    • does it power up?
    • does it light?
    • Does it respond to calibration gases?
    • Does the case heater work?
    • Does it seem to be contaminated?
  • We extract all of the restrictors and the one capillary, and test them for performance against the OEM’s specifications.
  • We do a clean up of the interior
  • We repaint the lid
  • we update the Preamplifier Board with new wires and connectors
  • we replace ribbon cables
  • we replace out-of-specification restrictors  / rebuild the sample capillary
  • we reassemble, light, test, calibrate, and run for 24 hours on a data acquisition trend
  • we attach calibration stickers and optimized pressure settings stickers
  • we write up a service report
  • then it’s boxed up and shipped according to your specifications

If you get the analyzer back and find that something is not quite right, PLEASE CALL US. It could be as simple as a loose burner cap, or ribbon cable came loose … something out of our control after it leaves our facility.

We sincerely appreciate your business and trust in our company

 

Keywords: Rosemount 400A troubleshooting

Won’t zero

Here’s a little background (with respect to mixed fuel analyzers only):

  • When the analyzer is in pristine (new) condition, the zero potentiometer is almost at 10 turns (100%) on the duodial (turns counter).  This is where the electronic compensation (for contamination) is at a MINIMUM.  Rosemount designed it this was so that turning the pot CCW also caused a decrease in the display value (it’s a little easier for the human brain to comprehend, that is, going CCW causes something to decrease).
  • We release repaired analyzers with the zero pot anywhere from 5 turns (50%) to 9.8 turns (98%); we strive to get the highest reading possible (which implies minimal contamination)
  • RIGAS usually upgrades the 400A Preamp board by replacing the unshielded burner signal wire with a coax (shielded) wire.  This helps reduce noise but also makes the signal so clean that we have to install a special potentiometer to inject a small biasing signal.  [link to R20 modification]

 

Here’s a little background (with respect to pure fuel analyzers only):

  • When the analyzer is in pristine (new) condition, the zero potentiometer is anywhere between 5 turns (50%) and 8 turns (80%) on the duodial (turns counter).  The pure fuel analyzer is WAY more sensitive so any minor contamination easily shows up and needs some zero pot to compensate.  10 turns (100%) is where the electronic compensation (for contamination) is at a MINIMUM.  Rosemount designed it this was so that turning the pot CCW also caused a decrease in the display value (it’s a little easier for the human brain to comprehend, that is, going CCW causes something to decrease).
  • We release repaired analyzers with the zero pot anywhere from 4 turns (40%) on up; we strive to get the highest reading possible (which implies minimal contamination)
  • RIGAS usually upgrades the 400A Preamp board by replacing the unshielded burner signal wire with a coax (shielded) wire.  This helps reduce noise but also makes the signal so clean that we have to install a special potentiometer to inject a small biasing signal.  [link to R20 modification]

 

When a 400A (or any hydrocarbon analyzer) won’t zero, do these checks:

  • Read flame temperature.  It should be around 100mVDC.
    • if it’s <50mVDC then you’re probably running hotter than you should be.  Decrease fuel pressure and watch for the change in zero reading.
    • if it’s <5mVDC then you’re probably running VERY HOT and in danger of melting the Teflon burner jet.  Decrease fuel pressure ASAP.
  • Alter fuel pressure to see if a few pounds pressure changes the reading (there will be a change as talked about above but it should be slight).
    • if the change is significant, you may have contaminated fuel.
    • if the change is significant, you may have the WRONG FUEL.  A cylinder of 40% hydrogen / 60% Nitrogen (or Helium) is NOT THE SAME as FID ION FUEL (40% hydrogen / 60% Nitrogen (or Helium)).  FID ION FUEL has a cylinder assay where the hydrocarbon contamination is VERY low, maybe even listed as “undetectable”.
  • Alter burner air pressure to see if a few pounds pressure changes the reading (there should only be a MINIMAL change, if any).   This statement is null and void if your analyzer is running right at the stoichiometric point such that decreasing pressure affects the actual flame due to oxygen starvation.
    • This problem will sneak up on you with an aged analyzer as the air restrictor clogs up over many years of service;  you’ll set the air pressure to 15# (per the OEM manual) but the burner won’t actually be getting the prescribed 450 cc/min of burner support air.
    • An analyzer running at stoichiometric will be hard to zero and hard to span.
  • Alter sample pressure when flowing zero gas.  You should expect some variation in the readings but nothing significant.  If the reading does change by a huge amount then sample line contamination is almost guaranteed.
    • If your process contains a ‘sticky’ hydrocarbon molecule such as Toluene, then expect significant delay times to achieve a good zero as it will take time for the Toluene molecules to detach from the sample transport tubing walls.

 

 

Keywords: Rosemount 400A troubleshooting

 

Readings are unexpected

This symptom shows up in different ways:
The readout shows an upscale reading with no flame present:

This unexpected reading is usually indicative of electrical leakage within the burner assembly.

The analyzer displays a loss in sensitivity, i.e, the same concentration of test gas reports a lower measured concentration over time:

This is often indicative of regular system degradation over long periods of time; the fuel and air supply systems (filters, restrictors, etc) as well as the sample restrictor and capillary can develop clogging, and the electrical elements of the burner can be partially short circuited, by extended operation without cleaning and rebuilds on the pertinent systems.

 

Keywords: Rosemount 400A troubleshooting

Won’t span

(Describe likely diagnoses and specify possible confirmation testing, mitigation, and relevant RIGAS products or services)

 

Keywords: Rosemount 400A troubleshooting

Won’t light

Failure of the burner to ignite can be attributed to several separate (or contributing) factors.

Ignition failure can be due to issues with the supply gases: an insufficiently purged fuel supply, pressure regulators for the air and fuel supplies adjusted incorrectly or simply malfunctioning, or flow restrictions of the fuel and/or air into the burner assembly caused by clogging.

It can also be caused by internal electrical problems, such as faulty contacts and connections in the ignition circuit.

Finally, it may be caused by malfunctioning or failed components, such as the igniter itself, the transformer circuit, or the ignition switch.

 

Keywords: Rosemount 400A troubleshooting

No analog output

(Describe likely diagnoses and specify possible confirmation testing, mitigation, and relevant RIGAS products or services)

Keywords: Rosemount 400A troubleshooting

Display reads “+1”

The “+1” reading is indicative of an out-of-scale sensor response.

The 400A readout is a “percent of scale” display, which means that the display reads out the percentage of the scale of readings available under the current range setting.

If the analyzer’s current output voltage exceeds 200% of the current scale, the readout will return “+1”.

A quick check of the actual current sensor output is to increment the current range selected upward until the sensor output is no longer out-of-scale.   The set range multiples* (see: 400A Calculator) are instructive in determining the real sensor reading.

*Range multiples are variable if the optional 400A range trim board is installed.

 

Keywords: Rosemount 400A troubleshooting

Unstable Readings

Unstable or noisy readings may be symptomatic of a contaminated flow system.  Hydrocarbon contamination can occur in multiple areas: external components, like the fuel or air supplies, external frits and filters, regulators or supply tubing; internal flow components, such as pressure regulators and gauges; and finally, with water or condensation infiltration of the burner itself.

Contamination issues can be mitigated with intensive cleaning of the suspect components, or with their replacement.

 

 

Keywords: Rosemount 400A troubleshooting