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:
- Noise on range X1 should be minimal (±1 count)
- All ranges should be correlated (especially those with an optional range trim board)
- Response to certified calibration gas should be equal to or better than factory specifications
- When TP5 = 5 VDC then [a] the display reads 100.00,  analog output is either 100mV or 1V or 5V (depending on jumper configuration,  isolated current output = 20 mADC
- Analyzer is clean
- Insulation is re-glued
- Frayed wires are fixed
- Plexiglas is grounded
- A/C power switch leads are coated with “liquid electrical tape” to prevent inadvertant electrical shock to the end user
- Ribbon cables are pristine
- Rear terminal strip has a sticker that shows what functions are on what terminals
- Zero pot (potentiometer) is greater than 50% (the higher the number here, the less contamination in the analyzer tubing)
- It needs to look good again (paint job if necessary)
- Flame safety circuits MUST work properly
- Backpressure regulator works as designed (and controls at a very reliable value)
- 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.
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).
Where used: 400A,755,755A,755R,870
Static sensitive: This board is not very susceptible to ESD but handle it with some ESD protocols.
Replaces: Rosemount 620433 (in kit p/n: 621023)
Compatibility: RIGAS has released its compatible version of the OEM board. Some nice enhancements were included:  hook-type test points,  better labeling,  heat sinks,  zero & span potentiometers can dual configuration (i.e., adjustable from the top or from the front).
Please specify potentiometer type when ordering. Choices:  end adjust or  top adjust
Typical failure modes (after many years of service):  total failure: most likely due to the fullwave bridge rectifier or output opamp.  non-linearity: most likely due to the charge pump circuit.  inability to calibrate: most likely due to the charge pump circuit.  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.
Repairable: Yes! Call us at 877-616-0600 for an RMA number.
RIGAS can save you money on desiccant cartidges by regenerating your saturated cartridge for half the cost of a new cartridge. Although not all cartridges can be serviced, the popular 1647727 from Parker can. This part number is used often in hydrogen generators for FIDS. Send us your used cartridge and we will restore it to like-new. Your desiccant cartridge will be returned to you in a moisture proof container ready for its next rotation.
We spent a few hours trying to route signals through the backplane (motherboard) so now we have a marked up copy. We don’t have it digitized yet, so just call us and we’ll send you what we have.
Other 316RA schematics (available at Teledyne’s website):
The 316RA is a trace oxygen analyzer (polarographic; chemical cell; fuel cell). It seems well built. It has wide acceptance of industrial customers.
These coolers/chillers are probably hard to come by … and if you do find one, it is most likely VERY EXPENSIVE. We can fix these. The usual failure mode is that your 951A (LoTempCo version) or 951C starts misbehaving and it seems to misbehave based on room temperature. It could also be impossible to zero or maintain a good zero. What is probably happening is your PMT (655168) is no longer being maintained at 6°C and that is creating a significant ‘dark current’ in the PMT. Or equally bad is that it is close to 6°C but the temperature is not stable, so getting a good zero on the instrument is fruitless.
Another failure symptom is scorched or burned wires associated with the chiller circuit. The chiller is fed by a high current DC power supply (roughly 14 VDC); when the Peltier chips go bad, more current is required to achieve the cooling required and ultimately, there is so much current that the wire limitations are exceeded (especially when you factor in Rosemount’s use of 18awg high current wire). Look at the J16 plug and the J15 plug on the Power Supply Board. Check the terminations on the terminal strip on the side of the high current power supply too.
The cooler is built with a metal can liner that surrounds the PMT; the metal liner is thermally connected to two Peltier chips (or elements); the Peltier chips are thermally connected to the aluminum fin housing that you see when you open the instrument. These components are all potted in Stryofoam insulation.
Check the continuity of the red and black wires going to the chiller unit. New Peltier chips will read about 2 ohms in one direction and -2 ohms in the other direction (the negative reading come from the battery effect of the Peltier chips; essentially these are a million thermocouples amassed together … and thermocouples are little batteries in the presence of heat).
Our repair consists of extracting the old Peltier cells, installing new ones, repotting everything, checking the feedback thermistor, and testing the final assembly.
Call us for more information.
Operation (excerpted from 400A manual): The ionization current generated by the burner is measured by an electrometer preamplifier located adjacent to the burner assembly. This small current is amplified and transformed into a signal voltage that is then further amplified by a post amplifier before being converted to a digital display suitable for direct data presentation. To cover the required dynamic range, the amplifier is provided with two gain ranges that differ by a factor of 100. Output voltage from the preamp is a precise function of ionization current. The most sensitive gain range includes a trim adjustment so that inter-range correlation can be obtained over the entire signal span.
A buffer signal offering unity gain and noise filtration provide a low output impedance to drive the signal cable and post amplifier circuits on the main circuit board. Selection of the low or high range feedback resistors is made by relay K1 on the preamplifier board. A variable offset current is injected into the summing node of the electrometer amplifier to compensate for background offset current. These currents influence the measurement procedure, and a variable voltage at the front panel allows the user to visually cancel these currents during the calibration procedure. Background current is due to unavoidable traces of carbonaceous material introduced into the burner flame by the fuel gas and air.
Operation comments by RIGAS: K1 is a N.O. relay (shelf state). When open (de-energized), maximum feedback resistance is applied to U2 (first stage) thus resulting in maximum gain or high sensitivity. When K1 is closed (energized by +5 VDC when range X100, X250, or X1000 is selected) then R17 is placed in parallel with R18 resulting in less feedback resistance and thus less gain or less sensitivity.
Jumper E1-E2-E3 should be in the E1-E2 position. E2-E3 is a factory test position but could be used to determine the exact amount of amplifier offset or burner contamination since all Zero Compensation would be removed from the circuit.
Jumper E4-E5 should be in place. This allows the polarizing voltage to be grounded out during lighting (when switch is set to “ignite”).
- Glass encapsulated, high ohmage, precision resistors get dirty. Dirt conducts so the more dirt, the less ohmage.
- Glass capacitors. Dirt conducts so more dirt changes capacitance.
- Coax cable breaks down (signals get noisy)
- Jumper wires get frayed, brittle, and break
- Opamps (operational amplifiers) fail (use list of expected voltages here)
- Purge / ignite switch fails
- 3 VAC transformer fails
- Interconnecting ribbon cable gets pinched and fails
- Burner contact assembly fails (this is a ghost [‘looks’ like] a preamp board failure)
- Burner collector ring connection fails (this is a ghost [‘looks’ like] a preamp board failure)
- Burner temperature sensor fails (fuel solenoid won’t stay latched after lighting ‘pop’)
RIGAS built a special resistor pack to simulate the ion current developed by burning hydrocarbons. We have six 500 gigaohms resistors in series to mimic the very low ion current (3 x 10-11 amps) in the burner (remember that a 90 VDC polarizing voltage is applied at this end of the circuit). This helps us determine if noise is coming from the burner chamber proper or the preamp board.
Schematic 620424 (with RIGAS embedded notes)
List of expected voltages
Simplified electronic calibration
- When the Zero pot is up near 10 (full CW) that is GOOD! That means that there is minimal contamination to overcome with a bias signal.
- Failure to light is usually a fuel/air ratio problem (usually not enough fuel getting to the chamber)
- Failure to light could be as simple a s blown glow-plug
- The 400A is a PERCENTAGE readout analyzer and a TOTAL HYDROCARBON analyzer
- the display reads a percentage of your calibration gas numbers
- any hydrocarbon will read out on this analyzer. If you calibrate with 20 ppm methane and inject 5 ppm of butane, you’ll get the same response
- Click here for the 400A calculator spreadsheet
- Replace old jumper wires & their connectors
- Replace coax
- Clean resistors and capacitors
- Replace DIP socket with gold plated DIP socket
- Replace opamps with latest low-noise opamps
- 620428 Rosemount 400A Main Electronics Board (schematic 620429)
- 620433 Rosemount 400A Isolated 4-20 maDC board (schematic 620434) … (item is now obsolete by OEM … replaced by RIGAS25C0007R0)
Situation: The analyzer appears to operate normally (mostly anyway). U13 seems to get very hot (so does U4 [voltage output buffer amplifier]) and there is a 620433 (V/I option board) installed. Also, when attempting to light the analyzer, the analog display will overrange and remain overranged until the power is cycled on the analyzer (TP-5 will be saturated at about 13 vdc).
Problem: someone has employed the E1-E2 and E3-E4 jumpers and this is causing a nasty feedback loop that U13 is trying to compensate for. When the analyzer goes upscale (it always spikes during startup) this causes the analog signal to spike which, in turn, causes the 4-20 maDC card to spike. The 4-20 signal being fed back to U13 has now locked it railed high.
Resolution: remove the 4-20 maDC board or remove the E1-E2 and E3-E4 jumpers.
Other info: U12 & U13 & U4 are µA714 opamps (a.k.a., uA714); they can be replaced with OP07 or OP77 or OP177.