Obsolete Parts and Analyzers

These are parts and analyzers that are no longer available or have become obsolete.  RIGAS is often able to still service these items though.

755, 755G, 755A, 755R, and 755EX are NOT obsolete!

It is true that the OEM has discontinued sales and support for these analyzers … however, they are still VERY viable!! As long as there is a vendor that can supply photocells, source lamps, and miscellaneous other parts, you should be able to count on your Rosemount/Beckman paramagnetic oxygen analyzer for decades to come.  Yes, decades!  As long as you (or your technicians) don’t over-pressurize or overflow the actual detector (dumb-bell assembly) then you should expect many, many years of service.

Typical failures that we see in our depot include:

·    blown thermal fuses,

·    bad power supply circuits,

·    wrong heater setpoints,

·    bad fans,

·    bad analog (or digital) meters,

·    bad 4-20 mADC boards, and

·    sometimes blown detectors.


With the exception of the “blown detector” issue, RIGAS can repair everything else!!

So what if you do blow up your detector?  Well, for about $6500, RIGAS can install a new, better, more accurate, and more reliable paramagnetic detector.  It’s actually an approved factory upgrade; the old Anaheim detector (formerly produced at the Rosemount facility in Anaheim, CA) is removed and a ‘buy out’ detector is installed in its place.  This newer detector is much more forgiving of excess flow or excess pressure events; plus it’s more accurate and less noisy.  You’ll need to wrestle with the cost though.  We believe that it’s right at a cutoff point where a brand new analyzer should be considered.  So let’s weigh the pros and cons:

[1] it will look and feel like the old analyzer so re-training is minimal,

[2] it’s still 100% Beckman/Rosemount and supported by RIGAS,

[3] there’s no labor time required to redo the panel cutout, plumbing, wiring, MOCs, etc, etc. (that just might be the savings that justifies keeping the old unit!!)

[a] it is an old analyzer with aging capacitors that are drying out … it will require some servicing before a brand new analyzer might require servicing … capacitors are easy to replace,

[b] cost of this new detector is high but it might be well worth it if you only end up spending $7000 to save the purchase price of a new analyzer at $20,000.

Call us. We can help!


620433 isolated 4-20 mADC board (sold in kit 621023) … possibly obsoleted by OEM … replaced by 25C0007R0

Description: This is an isolated signal analog output card used industry wide. The analyzer’s potentiometric output (DC volts) signal drives the signal for the 4-20 mADC card (usually 0VDC input = 4 mADC output & 5 VDC input = 20 mADC output). The term “isolated” refers to the fact that the output signal is not referenced to earth ground and is therefore much less susceptible to interference from other voltage sources. Milliamp signals are very useful when running long signal loops (on the order of tens of feet to thousands of feet long; note that total loop resistance has to be less than 850 ohms).

The board is built and tested as 620433. Rosemount packages this board in a kit (p/n: 621023) that contains the 620433 plus an instruction sheet & hold-down screw.

This is an excerpt from the Rosemount 755A instruction manual: An isolated current output is obtainable with the optional Current Output Board, either included with the Model 755A or added at a later date in the field. This option provides a current output of either 0 to 20mA or 4 to 20mA for a maximum of 850 ohms.

Where used: 400A,755,755A,755R,870

Typical failure modes:

  1. total failure: most likely due to the fullwave bridge rectifier or output opamp.
  2. non-linearity: most likely due to the charge pump circuit.
  3. inability to calibrate: most likely due to the charge pump circuit.
  4. noisy output: output opamp is failing –or– input signal is noisy –or– board mounted isolated power supply(ies) are failing –or– loop resistance is very high –or– it could be that your mADC reader (DCS, DAS, etc) is misbehaving.

Static sensitive: This board is not very susceptible to ESD but handle it with some ESD protocols.

Repairable: Yes! Our flat rate fee is $350 and assumes that we won’t have to replace the $250 Burr Brown isolation amplifier (we haven’t had to replace one yet!). Call use for a RMA number … 877-616-0600.

** (Pricing is valid through October 1, 2012) **

Replaced by: P/N: 25C0007R0 … RIGAS has released its compatible version of this board. Some nice enhancements were included: [1] hook-type test points, [2] better labeling, [3] heat sinks, [4] zero & span potentiometers can dual configuration (i.e., adjustable from the top or from the front).