Month: September 2020

Quarterly audits should be simple … thorough … but still as simple as possible. Unlike the Teledyne procedure (see below), our method is fully compliant with EPA Method 203, EPA Procedure 3, ASTM D 6216-98, and 40 CFR part 60.

This is a snippet of RIGAS’ procedure:

[1] record the serial numbers
[2] challenge the PLCF
[3] note the Fault indicators
[4] record current readings (including Dust Compensation)
[5] record current calibration values
[6] record calibration set points
[7] record LED drive current
[8] check purge air system (replace air filters as necessary [be careful not to disturb the dust, that will alter your EPA data])
[9] align
[10] perform a dust accumulation test (which cleans the optical surfaces as a PM measure)
[11] manual calibration cycle check
[12] record new Dust Compensation value
[13] install Cal Kit Fixture
[14] do NOT perform Background Set
[15] do NOT perform Normal Set
[16] do NOT remove Cal Kit Fixture
[17] do NOT perform Zero Set
[18] check Cal Zero value
[19] do NOT manual calibration cycle check
[20] analog output check
[21] perform Calibration Error Test
[22] record all EPA data from the data historian (or chart recorder)
[23] clean the unit (outside)
[24] complete the EPA compliant report

Please contact us if you’re looking for a vendor to do quality EPA audits, analyzer preventive maintenance, analyzer repair (on site or in our depot),parts, or telephone technical support. We also have Teledyne LightHawks to rent.

If asked how we would supply a sample source to a ‘pressure sensitive’ analyzer, we would tell you to control the source pressure and not throttle the source pressure/flow.

We’re in the “control the source pressure” camp and not of the “throttle the source flow” camp.  The Rosemount 400, 400A, 951A, 951C, 951E, NGA-FID1, NGA-HFID, and NGA-CLD series analyzers are sample pressure dependent analyzers, that is, this type of analyzer utilizes sample source pressure to create the motive force for sample to flow through a restrictor or capillary (amd in rare instances, through a mass flow controller).  In order for this type of analyzer to determine the % (percent) or PPM (parts per million) concentration of its sample, it requires a stable pressure at key pneumatic junctions within the analyzer itself.  Typically, this junction is near the sensing element and is usually a capillary tube or precision restrictor. To ensure that this pneumatic junction is controlled at some value, 3 psig for instance, a back pressure regulator (BPR) is employed.

This is how it is supposed to function: when sample is applied, the pressure within the analyzer builds until it reaches the control point (a.k.a., set point) of the BPR; if the pressure continues to build, the BPR bleeds the excess pressure off to a vent header or waste dump.  The bleed off is sometimes referred to as bypass flow.  This action by the BPR controls the pneumatic junction at a predefined value … as long as there is excess source pressure.

If we control the source pressure (i.e., sample pressure) then we can control the bypass rate as well, simply by changing the source pressure, that is, you control the delta-P (delta-pressure) between the two systems … and you get the benefit of great analyzer accuracy simply due to more accurate control of the key pneumatic junction.

Here are examples (assume that your analyzer runs at 3 psig internal sample pressure):

 

Example 1:

• Source pressure = 3psig
• Analyzer is happy (that is, the capillary is maintained perfectly at 3psig by either the internal backpressure regulator [BPR] or the external forward pressure regulator so the THC calibration is valid)
• But there is no bypass flow so response time to process excursions is VERY poor.

 

Example 2:

• Source pressure = 5 psig
• Analyzer is happy (that is, the capillary is maintained perfectly at 3 psig by the internal backpressure regulator [BPR] so the THC or NOx calibration is valid)
• and because there is a pressure delta between source pressure and control pressure, there is significant bypass flow (within the capabilities of the BPR) so response time to process excursions is good
• let’s assume that this creates 1200 cc/min of sample bypass flow (this assumption used in the next example)

 

Example 3:

• Source pressure = 4 psig
• Analyzer is happy (that is, the capillary is maintained perfectly at 3 psig by the internal backpressure regulator [BPR] so the THC calibration is valid)
• because there is a pressure delta between source pressure and control pressure, there is significant bypass flow (within the capabilities of the BPR) so response time is OK
• we probably lost half of our bypass from the previous example so let’s assume that this creates 600 cc/min of sample bypass
• We’re still OK.  No loss of accuracy. Response time to process excursions might be an issue on some systems.

 

Example 4:

• Source pressure = 25 psig
• Analyzer is NOT happy. The internal backpressure regulator [BPR] is bypassing at its maximum rate (with a nasty “singing” sound) and has lost control of the 3 psig at the sample capillary so the THC or NOx calibration is NOT valid).
• But there is significant bypass flow so response time is good … it’s just not giving us valid readings!
• All process readings will read much higher than normal, and thus, inaccurate.

 

This might be a good time to talk about regulators and back pressure regulators. It should be noted that as source pressure climbs from setpoint to the end of the control band of the regulator, there will be a slight upward creep of the control pressure value; this in turn affects the key pneumatic junction and the analyzer’s calibration curve. This has to do with the internal operation of the regulator.  In order to correct for something like this, you might have to invest in a digital controller and I/P module to control the dome loading of a specially designed regulator (one that controls pressure mechanically but will also accept an external pneumatic signal to bias its setpoint one way or another).

Some companies throttle the inlet and ‘hope’ that the capillary is maintained at the correct pressure.  You ‘could’ assume you have positive control of the capillary pressure by virtue of the fact that there is bypass flow.  But we’ve seen significant interaction between a throttled source and the internal control pressure (BPR); so much interaction that we don’t endorse this method of control.  It’s a method of control that will not yield the most stable calibrations or process readings.  So if you’re looking to get superior accuracy, control the source pressure and let the delta pressure (D/P) control the bypass rate.

Attempting to control the bypass rate at the back of the analyzer at the analyzer’s bypass exhaust port is very bad. This will essentially take the internal BPR’s control out of the equation … you won’t have any positive control of the pressure at the capillary head … so your calibrations will be at the whim of the source pressure (or source flow … which in turn creates a pressure).

We’ve always wanted to make YouTube video of this and put it out there to dispel all of the misinformation.   Watch for its release which will star Rachel Ward (Dead Men Don’t Wear Plaid) as Juliet.

Call us at 877-616-0600 if you want the verbal version!  (Just in case the written version doesn’t make any sense!)

We plan to write an article about this soon, but in the interim, here are a few bullet points:

* this is also referred to as Method 9 (found in 40 CFR part 60)
* there are many, many criterium required to perform a ‘legal’ visual observation
– time of day
– relative humidity
– temperature
– wind direction
– sun position
– weather conditions
– status of your EPA VEO certification
– distance to emission
– angle of incidence
– background contrast used
– white smoke or black smoke
– (will look up the other criteria and post it here)

Background: The 105% indication and reading is Rosemount’s way of showing an error message; it was presumed that everyone in the opacity business would recognize that there is no such thing as 105% opacity and that it would instantly mean ‘analyzer failure’ to anyone observing it on the monitor’s display. It was also an easy way to get the milliamp output signal to rail high at about 21 maDC.

Components affected: LCW (liquid crystal window), lamp (bulb), power supply (SLB, Stack LON Board), G-64 LON Board, interconnecting cabling, & temperature.

The fault alarm (105% opacity) can come from any of the following:

1. failing bulb/lamp or lamp power supply
2. failing LCWs or LCW power supply
   •  VLTH [volts too high]
   •  LMPF [lamp failure per software algorithm]
3. loss of Eshelon communications (LON)
4. failing wire harness (to lamp or LON communications)
5. failed calibration
6. corrupted software on the Stack LON Board
7. failing detector board (±15 vdc power comes from the SLB)

But not:

1. actual stack opacity conditions (high opacity)
2. misalignment
3. dust on barrier window and/or corner cube
4. steam that has changed phase to vapor

Call us to help you diagnose this. Please provide the following:

• model number
• age of LCWs
• age of bulb/lamp
• reference voltages (8) (under Cal, Reference Voltages)
• current ‘run’ voltages (4) (under Data, Volts)
• temperature

Your opacity analyzer normally runs fine, but then cold weather sets in and now the opacity readings are a bit flakey, spiky, noisy, weird, unusual, annoying, etc. Well, you should initially rule out the opacity analyzer … it’s not its fault! It’s probably physics! Or earth sciences! But it’s not sunspot activity.

What is most likely happening is:

• Your stack has significant moisture in its effluent
• Your purge air system for the opacity monitor draws makeup air from the very cold ambient air
• When the very cold ambient air meets the very hot, moist stack effluent, the effluent temperature drops significantly

…which…

• forces the relative humidity to approach 100%
• then forces steam (water) molecules to coalesce (condense) … a phase change
• then creates visible (water) vapor (some say ‘steam’ but it is really vapor)
• if you can see it, so can the opacity analyzer’s stack light beam

So, how would you prove this before investing any money in the solution?  How about a very simple test:

1. Somehow stop the purge gas flow temporarily

• •     block or partially block the blower’s (or blowers’) suction(s)
  •     turn off the blower(s)
  •     remove the feeder hose(s) to the injection ports

2. Observe your opacity readings for five to 30 minutes

• •     did the spiking go away?

3. Re-employ the blower system

• •    did the problem return?

If answers to questions 2 and 3 are “yes” then you have “Phase Change”

So, how do you fix it? Here are a few ideas:

• if it only occurs once in a Blue Moon, just declare it on your quarterly reports and take it as “down time”
• if it happens too often, your Regional EPA won’t enjoy seeing a high down time number
• install ducting so that the opacity analyzer draws makeup air from a warmed room
• install purge air preheaters (1500 watts per side minimum; 3000 watts per side for extreme conditions)

Call us at 877-616-0600 to discuss this in greater detail.

There are only two significant things to consider when installing LCW#1 in the OPM2000, OPM2000A, OPM2000R, or OPM2001: [1] over-tightening and [2] stand-offs.

When attaching the LCW to the transceiver’s mounting block, don’t over-torque or over-tighten the four (4) hold down screws. We always recommend “finger tight plus a skosh” (meaning finger tight plus just a tad (smidgen) more). The stack-up is normally in this order: aperture plate – stand-off – o’ring – backing plate (large holed) – LCW – top plate (small hole) – o’ring – screw head. An alternate stack-up can be in this order: aperture plate – stand-off – LCW – top plate (small hole) – o’ring – screw head.

The stand-offs are a factory modification and VERY important to the life span of the LCW. By putting the LCW 3/4″ away from the aperature plate, the beam has a chance to disperse and thus more of the actual LCW active surface area is utilized. This helps prevent “burning” the center out of the LCW (see picture). This is very critical in the OPM2001 as its high intensity beam from the 20 watt halogen lamp will cure the filler material and damage the LC event sites.

Stand-offs promote stability too because more liquid crystal event sites are being utilized if the beam is allowed to spread; as the LCW ages, LC sites tend to lock either open or closed, so if the beam is relying on 1000 events sites instead of 1,000,000 event sites, it will ‘seem” to become unstable sooner as event sites fail due to normal aging.

Parts:

LCW#1: 40F0050R02

 

LCW holding screws: 4-40 socket head, black anodized screws typically

Stand-offs:  4-40, 3/4″, aluminum, hex barrel, male-female

(LC stands for liquid crystal)

Components affected: LCW, liquid crystal window, lamp, barrier window, alignment, bulb, & temperature.

High opacity can come from any of the following:

1. actual stack opacity conditions
2. misalignment
3. failing bulb/lamp or lamp power supply
4. failing LCWs or LCW power supply
5. dust on barrier window and/or corner cube
6. steam that has changed phase to vapor

Call us to help you diagnose this.

Please provide the following:

• model number
• age of LCWs
• age of bulb/lamp
• reference voltages (8)
• current ‘run’ voltages (4)
• temperature

Communication failures typically fall in to 2 categories:

1. bad interconnecting wiring
2. board faults

If you’re not using Belden 8162 or 8163, you run the risk of causing a communications problem that gets worse with time.

The LON originates on the Stack LON board AND the IG-1 serial gateway. If either board is faulted, unpowered, corrupted, blown power supply,  or whatever then you’ll get COMM FAULTS.

Call for more details.

Communication failures typically fall in to 2 categories:

1. bad interconnecting wiring
2. board faults

If you’re not using Belden 8162 or 8163, you run the risk of causing a communications problem that gets worse with time.

The CRU talks RS232 which then routes to a converter (RS232 to RS422) before the signal leaves the CRU. The transceiver receives the RS422 directly without a converter.

Here is the order of typical failures:

1. RS232/RS422 converter in the CRU
2. IO Plexor
3. CPU board in the CRU

Call for more details.

You’re not the first to complain about this! There is a way to “desensitize” both the zero and span pots. It’s usually the span pot that gives you the heartburn; when you just breathe on the pot and your reading changes a 1/2 percent … that’s when you should call us!