The 400/400A is a Total Hydrocarbon (THC) gas analyzer utilizing the flame ionization detection (FID) method of analysis. It’s an older style analyzer (see history tab) that has proven itself to be a 24 / 7 / 365 workhorse for process gas analysis. It is mainly a desktop analyzer (with four rubber feet) or panel mounted analyzer (no feet) that fits in a standard 19″ rack.
The analyzer runs on 120vAC / 60Hz and consumes approximately 125W at steady-state (mainly due to an internal case heater). The analyzer is warmed to help control stability of the analysis (using the theory that as long as the analyzer is controlled at a temperature higher than ambient then thermal stability is assured).
The analyzer had three major revisions. [1] standard 400A with a notch in the case where the process connections attach; [2] standard 400A with a square (rectangular) case (no notch where the process connections attach); and [3] new version of the standard 400A with a square (rectangular) case (no notch where the process connections attach) but with completely new circuit boards operating off of an internal 24vDC power supply.
ANNOUNCEMENT: As of September 30, 2023, the Rosemount 400A has been officially obsoleted by the 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. Look at the GENERAL tab for a bigger treatment of this announcement.
General
Dimensions 8.75 in. High, 18.75 in. Wide, 15.88 in. Deep
(15.25 in. deep behind the faceplate / starting at the rack frame)
Total Hydrocarbon (THC) is a measurement of the hydrocarbon content (aggregated, not specific to an individual HC compound) concentration in a measured sample.
A Flame Ionization Detector (FID) analyzer tests for the presence and concentration of select compounds in a gaseous test sample by ionizing the compound of interest with a controlled combustion reaction.
The 400A Flame Ionization Detector (FID) THC analyzer tests for the presence and concentration of HC compounds in a continuous gaseous sample by combining the sample with a fuel gas stream, ionizing the present hydrocarbons through combustion, and then measuring proportional charge produced by the presence of the ionized hydrocarbons in the sample.
The Rosemount 400A has been officially obsoleted by the OEM (Emerson – Rosemount Analytical) with NO OEM PARTS or FACTORY SUPPORT as of September 30, 2023. While we knew this was coming, it still hurts a little. For end-users, this little THC analyzer has been a 24/7/365 workhorse requiring very little maintenance year to year.
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
Fixable. We have new transformers.
4-20 mADC card gets noisy or fails outright
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.
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.
We build our own cables.
Sample capillary – it gets clogged over time causing a lack of sensitivity.
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.
additionally, if your application is unique, we can build a unique capillary.
Thermal insulation – it becomes unglued.
We replace the insulation where needed and/or reglue the old insulation.
Burner contact gets old and brittle, and eventually breaks causing a total loss of analyzer functionality.
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).
IN WORKS (Video Link – short operational overview video)
IN WORKS (Video Link – in-depth overview video)
Overview of the 400A (PDF) <<(Not the same as the above PDF?)
Need drawings? <<(See Drawings tab?)
Need assistance? <<(See Problem/Solution tab?)
History
First, there was the Beckman 400. This unit dates back to the 1970’s; it sported a heavy duty metal case, an analog meter, a bull’s eye flame status indicator, and the necessary electronics.
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Second, came the Beckman 400A with new electronics, a better preamplifier board, and a notched case (the fuel solenoid is exposed and hangs out the back). It was quickly renamed Rosemount 400A as this was during the transition of when Emerson/Rosemount acquired Beckman Industrial.
The third revision is our favorite, the Rosemount 400A (square case; no notch). This has the standard Main Electronics Board (one of two possible versions), the better Preamplifier Board (only one tried and true version that we know of), the better case heater assembly (a fan, heater, and dedicated proportional controller circuit board, and one of three versions of the Flame Safety Board.
The last version, the fourth and present version, sports miniaturization of the Main Electronics Board, 4-20 mADC daughter board, and case heater controller board. Everything is driven by a 24 vDC off-the-shelf DIN mounted power supply. The result was the Rosemount 400A . . . We know, it’s confusing. That’s why we call it the “Rosemount 400A-circa 2009 analyzer.” Here’s the link to that specific page.
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What’s next? How about the Rosemount 400R? It’s the 400A but enhanced and built by RIGAS, but sold through the vast Rosemount sales channels. You’ll have to ask your local Rosemount Sales Rep to ping on his upper management in order to make the 400R something to purchase. You’ll like it – it will have the same great little burner, same Brooks regulators, same Siemens-Moore Products backpressure regulator, similar pneumatics, and the same Rosemount Preamplifier Board. But beyond that, RIGAS is going to fully digitize the Main Electronics Board so that it can read out in percent of scale (as it presently does) or part per million (ppm) of any hydrocarbon molecule that you can think of. It will also have diagnostics to give the user some insight as to what’s occurring within the analyzer (temperatures mainly but pressures and key voltages too).
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.
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.
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.
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.
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.
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
The RIGAS 400A Calculator
The 400A Calculator is an interactive MS Excel spreadsheet for use in determining optimal operational parameters, settings, and expected readings, given user-entered details of the use application. The 400A Calculator spreadsheet is available for download below; please view the tutorial video for instructions on using the spreadsheet.
Download the 400A calculator here 400A_THC_response_calculator_r1
— 400A Calculator Video Tutorial (in production circa April 2022)
