Oxygen Analyzers

Oxygen analyzers provide valuable measurements in combustion control, process quality, safety and environmental applications. These are used in a variety of measurement scenarios including, but not limited to, boiler trimming in power plants, furnace optimization in refinery and petrochemical applications, process safety in vent headers, and product quality in ethylene production.

Yokogawa offers a full range of product solutions including an industry leading zirconia oxygen probe series, as well as a line of cutting edge tunable diode laser spectrometers. 


  • Yokogawa’s new TDLS8000 houses all of the industry’s leading features in one robust device. The platform design is for in situ measurements which negates the need for sample extraction and conditioning.

  • The ZR probe's in-situ measurement method does not require any process conditioning or extractive sampling. This reduces maintenance costs and allows faster measurement response to changes in the process.

  • The AV550G Multi Channel Oxygen Analyzer System allows for measurements on up to eight ZR22 probes simultaneously. The ZR probe's in-situ measurement method does not require any process conditioning or extractive sampling, reducing maintenance costs and resulting in faster measurement response to changes in the process.

  • The ZR202 transmitter/detector combines benefits of the ZR402 remote analyzer and the ZR22 detector into an intelligent, rebuildable, low-cost measurement device for in-situ humidity measurement.

  • The OX400 is a low level zirconia oxygen analyzer that is capable of measuring a wide range of concentrations, from 0-10 ppm up to 0-100 vol%O2.

  • The TDLS220 is specifically designed for accurate, reliable and low maintenance measurement of volume percent (vol%) oxygen (O2) for safety and process applications. It is a viable alternative to paramagnetic O2 analyzers.

  • Yokogawa's Zirconia oxygen detector systems offer a variety of calibration units for quick, easy control of calibration gases giving the user simple, accurate calibration.

  • WZ-H cables are compatible with all ZR22, ZR402, and AV550G model Oxygen Analyzer Systems. The purpose of these cables is to transmit the signal from the sensor/detector to the analyzer. Additionally, the cabling provides for electrical input to the heater assembly within the detector for cell temperature control.

  • The accumulation of fly ash on the zirconia cell affects its ability to measure oxygen concentration. Fly ash and its constituents can reduce the life of the zirconia cell and affect the cells response time to changes in gas concentration. Yokogawa's large surface area sintered metal filters are designed to keep particulate and ash off the measurement cell.

  • Yokogawa's CENTUM CS 3000 DCS Monitors and Controls Operations at Poultry Litter-to-energy Plant
  • The boiler and turbine startup procedures reduces operator workload and helps to ensure a smooth and safe startup

Meter Checks:

  • Heater: 57-85Ω (typical is 62-67Ω)
    • Typical failure is Open or shorted
  • TC: if the probe is at room temperature -  less than 3Ω, in the stack and hot less than 100Ω (it is a type K Thermocouple)
    • Typical failure is open or shorted to the case.
  • Cell negative wire to the case. It should be a direct short to the case. If resistance is above 5Ω it can cause intermittent/erratic readings.

Cold junctions:

  • RTD type (red/black or red/white wire)
    • Resistance approx. 1100Ω at room temperature, no polarity (2 wire PT1000 RTD). Typical failure is Open or shorted.
  • Transistor type
    • Checks out like a diode. One direction is high resistance (typically in the MΩ) then the other direction will be open. Typical failure will have high resistance both directions or low resistance in both directions.

High Voltage Tests:

Use a 500Vdc Insulation Meter Checks (Aka: Megger). Be sure there are no wires attached to probe before doing this test.

  • TC + to the case. Should be >2MΩ
  • TC – to the case. Should be >2MΩ
  • Cold Junction + to the case. Should be >20MΩ
  • Cold Junction – to the case. Should be >20MΩ
  • Both sides of the heater to the case. Should be >2MΩ
  • If the O2 cell is removed you can also check the Cell positive to the case. It should be >2MΩ

Testing O2 cell:

  1. Perform a 2 point calibration. Check the cell resistance (under the magnifying glass button). Consider replacing the O2 cell if it is higher than 1000Ω. Higher resistance means the response time is reduced and can cause calibration errors if the response is very slow. 
  2. Remove the cell + & - wires from the channel card.
  3. Place a short between the Cell + & - on the channel card.
  4. Turn power off and on with the channel card power under maintenance and allow the channel to come up to temperature
  5. Note: Channel should read ~21% and the reading should be stable. If the unit comes up with a cell failure or the reading is erratic the problem is in the channel card.
  6. Apply Zero and/or Span gas (500 cc/Min). Measure the loose wires at the electronics.
  7. Span Gas (instrument Air) should read close to 0 mV (+/- 5 mV)
  8. Zero Gas Should read as follows:

        0.4% O2        84 mV’s (75-90 mV’s)
           1% O2        67 mV (55-70 mV’s)
           2% O2        52 mV’s (45-55 mV’s)


For a multichannel converter (AV550):

  1. Be sure that the heater and signal cables are landed on the correct channel card.  If the heaters are crossed it can cause this. Try swapping a working channel card with the channel in question. If a different card works properly it is a bad channel card.
  2. Swap probe to a working channel.  If it works on a new channel and not on the old channel the power unit is damaged.

Temperature low or not heating up:

  1. Reset the channel.
  2. If the probe fails to warm up turn off the channel.
  3. Unwire the Heater, TC, and CJ and perform the ohm meter check on the Heater, TC , and CJ.
  4. If you find a failure in one of the above, go to the back of the probe and check them inside the probe housing.
  5. If there is not failure in the probe housing, but there is one at the electronics the problem is in the cable.
  6. If all the values check out in the probe then you need to check out the electronics.
  7. Reconnect the wires from the heater, tc, and cj.
  8. Reset the analyzer/channel, measure the voltage going to the heater. It should be 60-120Vac (Voltage is a modulated voltage but can be measured as AC)
  9. If power is not present check the fuses.
  10. On the AV550 they are on the power unit (just above where the heater wires up). There are 2 fuses per channel.

High Oxygen Readings:

  1. Check for a leak in in the calibration system or cal line.
  2. Remove the fitting from the probe where the calibration gas is connected. Replace it with a pipe plug with Teflon tape. If the problem goes away the problem is a leak in the cal gas line to the probe or in the autocal system.
  3. If the reading is still high it could be a leak inside the probe between the cal gas inlet and the end of the probe by the cell. Remove O2 cell. Plug end of cal line (You can flip the o2 cell over, place a small piece of rubber in between the cell and flange and install the cell to plug off the line). Apply a approximately 1 PSI to the cal line, shut the pressure off and see if it holds pressure.
  4. Bad O2 cell
  5. Run calibration. If cell resistance is above 200Ω replace the cell.
  6. If you get a cal error replace the cell.
  7. Cracked O2 cell
  8. Run Calibration. Apply zero gas at 500 cc/min max. If reading is not stable or it is reading high it is likely the cell is cracked.

Low Oxygen Readings:

  1. Leak in calibration system (AutoCal system or Manual Calibration Panel). 
  2. Plug off cal line at the back of probe. If problem goes away find the leak in the zero cal gas side of the cal system. Zero Gas may be leaking past a valve into the cell.
  3. Bad O2 cell
  4. Run calibration. If cell resistance is above 200Ω replace the cell.
  5. If you get a cal error replace the cell.
  6. Excess hydrocarbons (fuel)
  7. O2 probes control at 750°C, If the process has excessive hydrocarbons (un-burnt fuel) they can burn on the tip of the probe consuming the oxygen at the tip of the probe and making the reading go low.
  8. Excess moisture in process
  9. If excessive moisture is in the process it can come in contact with the O2 probe (750°C) and cause steam right at the O2 cell. If you have excessive steam at the O2 cell it will read low, as well as possibly damage the O2 cell.

Erratic Reading:

  1. Be sure heater and signal wires are in separate conduits.
  2. Flow zero gas at 300-500 cc/min on probe.
    1. If reading continually drifts up the O2 cell is cracked.
  3. Perform a calibration
    1. If readings are unstable and calibration fails see cell troubleshooting.

If you have set a password and have forgotten it you can use the password "MOON" to get into the configuration menu. Then you will be able to modify/view the password that is set in the unit. 

Note: if you have not set a password just hit enter on the screen and it will accept that as the password.



The password to get in all the maintenance and commissioning menus is 16 

ZR22S: Option "B" Adder

This is the Japanese GS sheet, containing a number of options we rarely sell here in the US. Contact Support at 800-524-7378 or support@us.yokogawa.com for price and delivery information. 



Yokogawa has been making Zirconia Oxygen Analyzers for over 30 years. The older O2 probes and analyzers used a transistor temperature sensor. The newer units use a PT1000 RTD. We discontinued the ZO21D probe and both the AV8G and ZA8C analyzers over 15 years ago. To make it easier for our customers who still had the older ZA8C and AV8G analyzers we added an option to allow them to order the ZR22G probes with the old style sensors already installed. Some customers are still ordering ZR22 Probes with the /ZR or /AV option (see the photo to the right). In many cases they are actually using them on AV550s or ZR402Gs but they have the analyzers set to “ZO21D” mode so that they will work with the old cold junction sensors. They were purchasing probes with the old sensor because they still had some ZA8C Analyzers or AV8G Analyzers in operation along with some of the newer ZR402s and AV550s.

Now the old style Cold Junction sensors are no longer manufactured, and we have not been able to locate another supplier.

These customers need to replace any ZA8Cs or AV8Gs they still have with ZR402s or AV550s.

The new Cold Junction sensor is a PT1000 RTD. It is available as a spare part. The part number is K9470BG - Cold Junction (RTD) for ZR22.

We have a limited stock of the ZO21D style cold junction sensors. The part number is E7042AU-J1, and the list price is $250.00. We will continued to sell them but they will be gone in a short time. The few customers that still have ZA8Cs or AV8Gs can purchase the parts but they need to plan to change to the ZR402 or AV550.

Identifying the Cold Junction Sensors

The Cold Junction sensor may be a PT1000 RTD or a Transistor Cold Junction sensor.

There are two styles of RTD that have been used. Both are PT1000:

The newer units have a PT1000 sensor with a Red & Black wire


The older units have a PT1000 sensor with a Red & White wire.


The Transistor sensor is mounted on a small metal bracket with 2 wires connected to one terminal and 1 wire connected to the other one.


For the ZR402G or AV550 with a PT1000 sensor set the Detector Setting to ZR22G.

For the ZR402G or AV550 with a Transistor sensor set the Detector Setting to ZO21C.


You can use the password JAVAJAVA to get past the password screen. Make sure you go to the password menu change the password setting. 

AV8C Channel reset code

You can use code 58 to reset a single AV8C channel. 

First scroll the display to the channel you would like to cycle, then enter code 58. 


Here's a link to download the AV8G Manual. 


The part number you see on the channel card circuit board is not the part number for the channel card. It is the part number for the circuit board before any parts are installed. 

There are 2 versions on the channel card. 

If you look at your channel card you will see there are either 1 or 2 blue "boxes" on it. 

If you see 1 Blue box your channel card has common Isolation - the part number is AV55M-A1

If you see 2 Blue boxes your channel card has individual isolation - the part number is AV55M-B1


The AV550 automatically turns off the power to the channel card when it is removed. You have to either cycle power to the whole unit, or use the channel card power. 

To get to the channel card power menu hit the Setup Key (wrench). See below: 

Select Maintenance 

Select Channel card power

Select the desired channel and enable. 


The password to access the maintenance and commissioning area is 77


Combustion furnaces such as heating furnaces and boilers in plants include various sizes and types, and serve as energy sources, that is, they are cores in all production activities. Because a large amount of fuel such as gas or fuel oil is consumed in plants, their combustion efficiency directly affects the performance and running cost of the plants. 

Información del Producto


    Yokogawa’s new TDLS8000 houses all of the industry’s leading features in one robust device. The platform design is for in situ measurements which negate the need for sample extraction and conditioning. The non-contacting sensor allows for a variety of process types including corrosive, abrasive and condensing. The first generation platform has been proven in many others for the measurements of O2, CO, CH4, NH3, H2O and many more NIR absorbing gases. This second generation platform has improved reliability and ease of installation and maintenance while still meeting or exceeding designed application demands.


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