NIHON KOHDEN Vismo PVM-2703 patient monitor (Feb 2011)

Category: NIHON KOHDEN Vismo bedside monitors and networking. In this article we review both the PVM-2701, PVM-2703 and PVM-4763 Vismo patient monitors, the thinking and illogical approach of the product series.

The First VISMO Monitors

The PVM-2701 model was announced by Signal 718 dated November 2009. Vismo came from Vital Signs Monitor. Notice this was the first model to do away with the suffix.

 

 

In a pilot move, the new Vismo series was designed in Japan with as many parts sourced in China. Although initial shipment were assembled and shipped from Japan, this arrangement was changed from release of PVM-2703.

 

 

 

The questionable act of exchanging two fixed-use connector sockets for one flexible common-use socket

 

The 7-parameter Vismo PVM-2703 was released in February 2011 equipped with a yellow flexible common-use socket for either Invasive Blood Pressure or mainstream etCO2 monitoring use. The prospective buyers should question the benefit of a flexible socket when there is shortage of one connector socket; do not focus on the flexible socket, but overall carefree flexibility. In addition, the measurement cables for the common-use sockets are not ordinary cables, and priced at a premium by the manufacturer.

From the release of PVM-2703, shipment for both PVM-2701 and PVM-2703 models started to be only from Shanghai, China.

The prominent feature of the VISMO PVM-2703 bedside monitor is the utilization of one common-use socket that is colored yellow and known as MULTI socket. This yellow MULTI socket is for dual-purpose use and does not accept ordinary measurement cables, but only measurement cables that have valid NIHON KOHDEN digital hexadecimal codes embedded in their yellow connection plug for IBP and mainstream CO2. The end result of using a flexible dual-purpose socket is the elimination of one fixed-use connector socket on the PVM-2703 bedside monitor, which actually led to usage inflexibility for users!

 

The bottom line is, if the users could have one fixed-use socket for Invasive Blood pressure and another fixed-use socket for mainstream CO2, that would be a far superior design since the monitor can now do all 7 parameters at once. What user benefit is the manufacturer trying to provide?

The archaic concept of a MULTI-PARAMETER UNIT (MPU) from the 1990s

 

Veiled in secrecy, NIHON KOHDEN does not explain to the market how they could make sockets that are flexible enough for five types of internal hardware, as well as being able to additionally used as a serial port. Almost all sales and marketing people employed in Japan Head Office have no engineering background, so there is no shortage of "company secrets" that should not be discussed with the distributors or customers.

Here are the relevant facts. Back in the 1990s,  NIHON KHODEN identified five types of analog hardware (Temperature, IBP, Cardiac Output, Thermistor Respiration, FiO2) that can be linked from the inside onto the yellow common-use MULTI sockets and to make use of these internal hardware, an external measurement cable with a valid digital code stored in its plug needs to be inserted into one of these communal MULTI sockets. These measurement cables that come with coded plugs are collectively cited as Smart Cables by the manufacturer and the embedded digital codes are also known as parameter-selection codes since it pinpoints the type of internal hardware needed by the measurement cable.

 

Each yellow MULTI socket selects only one channel of the internal hardware, except for Temperature allowing two channels of hardware to be selected.

 

One MULTI socket can select two Temperature hardware channels.

Each MULTI socket can take two channels of Temperature measurements

  

Note the hardware mentioned here (Temperature, IBP, Cardiac Output, Thermistor Respiration and FiO2) are linked to the yellow MULTI socket internally, and not from the outside

 

An external measurement cable with a valid digital code embedded in its plug selects the intended internal hardware (only if available)

The intended five types of hardware are grouped into an electronic community known as the MULTI-PARAMETER UNIT (MPU), complete with a small number of yellow MULTI sockets for communal sharing. Only Smart Cables with the necessary valid parameter codes can make use of the hardware placed in the MPU via the MULTI sockets.

 

The design rule dictates that all MULTI sockets must be capable of doing IBP monitoring, and each MULTI socket therefore has a dedicated IBP hardware attached to it.

Principle of operation

During use, a MULTI socket can only make use of its own dedicated IBP hardware when an IBP measurement cable is plugged into it. For non-IBP monitoring, the socket can access a common pool of Temperature, Cardiac Output, Thermistor Respiration and FiO2 hardware that are placed in the MPU for sharing, which all MULTI sockets can link to.

 

 

The design means the quantity of MULTI sockets in the MPU is not a number that can be decided at will, but must correspond exactly to the number of internal IBP hardware channels intended to be placed inside the MPU. 

Given the large amount of hardware in the MPU block, more MULTI sockets are needed to make good use of the hardware that would otherwise be idling in the MPU. As illustrated in the above image, this is achieved by using an external expansion box filled with more MULTI sockets (each with own dedicated IBP amplifier hardware).

The additional MULTI sockets are integrated using analog interface, and have to be limited to a maximum of four sockets to avoid signal deterioration caused by voltage drop and noise.

 

Professionally, many are actually puzzled by the contents of the MPU but refrained from asking or faced with a wall of silence, why is this a design that has many internal hardware queuing up to share a limited number of low-cost sockets? The truth is because it was originally devised to solve the problem of limited panel space area not sufficiently enough to mount all the necessary connector sockets. In situations when panel space area is more than enough to accommodate all the necessary connector sockets, there is no longer need for the MPU or communal connector sockets.

 

It is a waste of money to adopt such a design when the need does not exist. Its continued use regardless of need shows us there is more than meets the eye and the reason to question its relevance.

You can confidently tell there is only one channel of internal IBP hardware in the PVM-2703 from the number of functional MULTI sockets on the monitor

 

Knowing a functional MULTI socket always come with its own dedicated one-channel IBP hardware, a user can accurately tell the number of IBP monitoring hardware channels supplied with any monitor, just by counting the total number of available yellow MULTI sockets. 

The key word here is "functional" because a non-functional (fake) yellow MULTI socket does not need to care about the capability to do IBP monitoring, such a socket can be found on the CardioLife TEC-5600 series defibrillators. The fake yellow MULTI socket on said TEC-5600 series defibrillators is just a serial port dressed as a communal socket that cannot be used for any other parameter except mainstream etCO2 kit sets.

Variations to the basic theme

There are variations to the basic theme, such as

a. doing without use of external expansion box,

b. increasing the number of MULTI-parameter sockets in the MPU,

c. reducing the hardware configured in the MPU.

In the VISMO PVM-2703 bedside monitor, only one channel of IBP hardware is configured in the MPU, out of five possible hardware types for use by Smart Cables. This being a simple monitor, the expansion box is not necessary.

You can see the parameters NIBP, SpO2, ECG and one channel of Temperature on the Vismo PVM-2702 monitor are not using Smart Cables, they are therefore not part of the MPU.

The digital hexadecimal code is programmed into a non-volatile EEPROM chip (Electrically Erasable Programmable Read-only Memory) mounted on a small flexible PC board, and soldered to some pins of the yellow plug at the factory; users cannot change the code using settings on the monitors. It is not difficult to make the Smart Cables but they are being priced highly by the manufacturer; only the common IBP cable can be sourced from China suppliers at a reasonable price.

A non-volatile digital parameter code is embedded in the plug of the measurement cable

The communal yellow MULTI sockets are additionally diverted to serve as costly digital serial ports

As explained earlier, the design objective of MPU was to solve the problem of limited panel space area, further reduction of necessary sockets via use of MULTI sockets as serial ports will help towards this objective. This being an easy task since there is no need for additional internal analog hardware; the processed digital signals from the serial kit sets just bypass the analog stage and go straight to the digital processing stage of the monitor.

A mainstream CO2 serial kit set is linked to the VISMO PVM-2703 bedside monitor using a Smart Cable, treating the MULTI socket as a serial port.

The original label for the yellow MULTI socket indicated the five specific hardware and also serving as serial port for mainstream CO2 serial kits, the purpose was to minimize the number of sockets being used on a limited panel space.

 

The original label for the yellow MULTI sockets when they were first used

 

It is simple-minded to think the use of Smart Cables can actually upgrade a configured monitor to be modular
 

A yellow MULTI socket by itself does not automatically mean all the five types of mentioned parameters are available for measurements; it still depends on whether what hardware are actually being placed inside the MPU for selection by Smart Cables.

Additional parameter capability can be added using serial kit sets or via interfaces to external equipment.

When a model is not equipped with FiO2 hardware internally, no amount of yellow MULTI sockets is going to provide this measurement capability. The amount of configured hardware linked to each MULTI socket varies, so is the system support for serial kits and external interfaces.

Examples of configured hardware and serial kits using Smart Cables

 

 

It is the built-in hardware that determine the parameter capability; and in the case of serial kit sets, the system software. This of course, is the same description as a configured patient monitor

 

Actual internal hardware and system support for serial kits varies for each multi-parameter unit

Concluding, it is obvious VISMO PVM-2703 bedside monitor making use of Smart Cables is still a configured monitor. The customers are just being led into having an unrealistic expectation of what the Smart Cables and MULTI sockets can actually deliver.

The manufacturer chooses to ignore the captured value from using Smart Cables is negative for users

Without any use of Smart Cables, both one channel of IBP and one channel of mainstream CO2 are freely available for carefree use via their respective dedicated sockets. The use of Smart Cables just makes things unnecessarily complicated and requires deliberate operator choice to choose between IBP and mainstream etCO2, but not both! What is the benefit of having such a choice?

The output of the etCO2 kit sets are already-processed digital output data that should go straight to the DPU

The mainstream CO2 parameter is supplied as a self-contained serial kit set with already-processed digital output ready to go directly to the digital processing stage of the monitor; there is no need to compete for use of the MULTI socket with the IBP measurement cable.

Manufacturers make their profits by providing product benefits to users but the yellow MULTI socket in PVM-2703 bedside monitor has no benefit. In fact, socket shortage is the unintended problem for users having to share a dual-purpose MULTI socket for IBP and mainstream CO2.

What benefit can it offer users when necessary connector sockets go missing?

To be sure, it does save the cost of a cheap connector socket, but the cost to share the common-use sockets is far greater.

Elaborate time-sharing are applied to things that are expensive (high in demand, an asset), and not worth the efforts for things that are cheap (high in supply, a commodity) like a connector socket or a switch! It only makes sense to see productive efforts being made to time-share a CPU, a car, a hotel room, a yacht, an airplane but not a calculator, a pencil or a pair of scissors.

 

Time-sharing of a car (an asset) creates value

The next picture shows Philips time-sharing one channel bio-amplifier hardware between IBP and Temperature measurements, and there was no sharing of connector socket; this is exactly the opposite of what Nihon Kohden is doing. The said manufacturer merely ensures physically it is not possible to make use of both the PRESS and the TEMP socket at the same time, and the purpose is to make it possible for the same hardware to be used for different purpose at different time.

 

This design shares the expensive hardware, not the cheap sockets

There is no monitoring hardware embedded in the NIHON KOHDEN Smart Cables and this makes a big difference as to how you appraise a monitor that comes with MULTI sockets

 

In this section, we want to show beyond any doubt, there is absolutely no active electronics in the Smart Cables.

 

The marketing messages "New Modular Technology" and "The Module is in the cable!" are just the imaginations of people without the necessary electronics knowledge.

What do the manufacturer mean by this statement? 

It started with the Life Scope TR (BSM-6000) series monitors in the USA market and gradually adopted officially for International markets. These are precise statements.

The continued repetitions of an assertion without offering any proof does not make it the truth!

This is just wild assertion without offering any proof

 

Chip makers need huge demand to justify each of their products, so which chip manufacturer is supplying NIHON KOHDEN the variety of analog chips given the extremely low volume in demand? If we were to open up the plug of a Smart Cable, what do we see? A small PC board is seen being soldered to some pins of the yellow plug.

 

A small PC Board is soldered to some pins of the yellow connection plug

 

The PC board confirms a cheap non-volatile digital EEPROM chip is being used to code the Smart Cable.

 

A non-volatile cheap digital EEPROM chip was what we found inside the yellow Smart Cable plug

If we were to open up the plug of a compatible IBP cable from China suppliers, what do we see? It is the same thing, a plug with a digital code defined by NIHON KOHDEN.

Under US FDA rule, a cable is only a cable if it does not change the signal that passes through it. A Smart Cable with a hexadecimal code is just a cable and does not change a signal passing through it, but if it has an amplifier it becomes a medical device and requires FDA registration. Can you find any stand-alone NIHON KOHDEN Smart Cable registered with US FDA as a medical device?

Make no mistake, when the Smart Cables are used with serial kit sets, such as mainstream CO2 kit sets or the NMT AF-101P kit set, the registration is for the active serial kit set (just like any other manufacturers) and not the passive Smart Cable.

 

Irrefutable proof the IBP amplifier hardware is configured internally, an important fact withdrawn from later monitor manuals

The Life Scope BSM-2301 bedside monitor was launched before the Life Scope TR and Life Scope J bedside monitors, and the Service Manual is clear on the design; manuals for later models stop providing such information. The major move to curb details in manuals started from Life Scope J (BSM-9101) Bedside Monitor, which was launched before the Life Scope TR bedside monitors.

In BSM-2301 service manual, you can see the IBP and thermistor respiration are internal hardware inside the Life Scope BSM-2301 monitor. These hardware are clearly shown being linked internally to the yellow MULTI socket, and to make use of either hardware, a Smart Cable with the correct code must be plugged into the MULTI socket.

 

Can you see the IBP amplifier and thermistor respiration hardware are internal components of the Life Scope BSM-2301 monitor?

The MULTI socket doubles as a serial port without any need for internal monitoring hardware, only as a link to the monitor. In the block diagram below, the processed digital serial data from a CO2 kit set goes straight to the digital micro-controller APU (Analog-block Processing Unit) and is forwarded to the DPU.  For a parameter using the internal analog hardware, the analog signal needs to converted to digital before going to the APU for digital processing. 

Relevant page in the combined Service Manual for BSM-2301A, BSM-2301K, BSM-2303K, BSM-2304A

You should know by now the IBP amplifier hardware inside the monitor is the reason the VISMO PVM-2703 bedside monitor can do one channel of IBP monitoring, and that the IBP amplifier hardware is not embedded in the plug of the IBP Smart Cable.

 

Life Scope BSM-2300K series bedside monitors case study

Preceding VISMO PVM-2703 bedside monitor was the Life Scope BSM-2300K series monitors, let's see how this sole yellow MULTI socket was actually being used in this series.

 

The portable 8.4-inch Life Scope i (BSM-2301K)

 

To insist the use of Smart Cables, the Life Scope BSM-2301K monitor has a yellow MULTI socket flexible enough for three types of measurements, namely:

 

a. Invasive Blood Pressure

b. Thermistor Respiration

c. Digital self-contained mainstream CO2 serial kit sets.

 

Without any use of Smart Cables, all one channel of IBP, Thermistor Respiration and one channel of mainstream etCO2 are freely available for carefree use via their respective dedicated sockets. The use of Smart Cables just makes things unnecessarily complicated and requires operator choice to choose among IBP, Thermistor Respiration and mainstream etCO2, but not all. It is so obvious using three dedicated sockets is a far superior design!

 

We should ask why is there a need for users to endure the pain of two missing sockets in exchange for one flexible socket capable of connecting to three types of measurement cables? If MULTI socket is such a superior proposal, why is the Temperature socket a dedicated one?

 

Life Scope-i does not have enough connector sockets

 

The two blocks of patient monitoring hardware in the Life Scope BSM-2301 bedside monitor are:

CONVENTIONAL BLOCK

(The hardware only use dedicated sockets and ordinary cables)

- 1-ch TEMP

- ECG

- SpO2

- NIBP

MPU BLOCK with one yellow MULTI sockets

(The hardware only use Smart Cables for connections)

- 1-ch IBP

- Thermistor Respiration

- etCO2 <kit set using MULTI socket as a serial port> 

 

The reality is the shortage of two connector sockets, and users are all insisting the single MULTI connector socket on the BSM-2301K is not enough. The manufacturer was pressured to respond with an updated model an updated model, BSM-2303K. The solution from new model BSM-2303K is to add a new isolated yellow MULTI socket.

 

The MPU design in the BSM-2301K was not designed to take on expansion, and the isolation was needed not to load the operation of existing MPU. It means the additional MULTI socket is a fake one and only could make use of its own associated IBP amplifier hardware.

The fake MULTI socket was intended solely for IBP monitoring, effectively relieving existing functional MULTI socket to only measure either Thermistor Respiration or act as serial port for the mainstream etCO2 kit set. It was not a solution, as a logical one would be to do away with the MULTI sockets, but there was a need for the manufacturer to keep using the Smart Cables.

There was no actual demand for additional IBP channel in the targeted segment, but the manufacturer was cornered to declare BSM-2303 bedside monitor was a response to market demand for an upgraded monitor with 2 channels of IBP.

Under pressure, an additional isolated MULTI socket acting solely as an IBP amplifier had to be introduced

Similar to Life Scope BSM-2301 Bedside Monitor, the VISMO PVM-2703 Bedside Monitor was another disappointment

Just like BSM-2301 bedside monitor, users were not impressed and want their missing socket back on the PVM-2703 bedside monitor so that they can carefree IBP monitoring and mainstream CO2 measurement without the need to choose. In new PVM-4000 series bedside monitors, the VISMO PVM-4763, PVM-4753 and PVM-4733 are not exactly responding to what the user want.

 

The new series offer users two MULTI sockets, but if you had not missed the details earlier, each MULTI socket comes with its own one-channel IBP amplifier hardware. Thus, the VISMO PVM-4763 bedside monitor is adding one redundant IBP hardware channel just to do what the PVM-2703 monitor could already do if dedicated sockets were used instead. The user did not ask for an additional channel of IBP hardware!

There is just no reason to continue the use of Smart Cables except to meet the manufacturer's own agenda.

 

Beware the need for network isolation units to ensure electrical safety of monitored patients

For networking, the Vismo PVM-2701 and PVM-2703 need the QI-202P Interface option but the interface is not equipped with a isolated Ethernet LAN interface. When connecting to a real-time LAN network, it is important and mandatory for hospitals to observe patient electrical safety by using a network isolation unit.

 

When an isolated monitor with an non-isolated Ethernet port is connected to a hardwired network, it is no longer a medical device unless the above-shown network isolation transformer is introduced between the monitor and network. If the network isolation transformer is not installed, dangerous electric shocks can be delivered to a monitored patient through the wired Ethernet network. Such dangerous electric shocks are potentially lethal and no hospital should ignore this mandatory requirement.

WATCH OUT the dangerous use of semi-quantitative CO2 measurements and ignorantly displaying a flawed CO2 waveform

Nihon Kohden lacks sidestream CO2 sampling expertise and buys OEM units to offer them as expensive standalone. The AG-400 CO2 unit as shown, for example, is technology from Oridion Medical. For monitoring such as post-surgery recovery, integration of the sidestream CO2 into the monitor is a mandatory requirement because an external unit requires additional power socket besides necessitating the use of a trolley.

 

For some unknown weakness, Nihon Kohden monitors have never been able to offer benefits of integrated sidestream CO2 measurement.

 

The inability to integrate the sidestream CO2 unit into the patient monitor main unit

The adoption of semi-quantitative mainstream CO2 measurement was to reduce cost and its simplicity also help in miniaturization of the transducers. The first solution offered by Nihon Kohden was the mainstream cap-ONE TG-920P CO2 sensor kit (order code P907) that can be used on non-intubated patients.

 

The cap-ONE TG-920P CO2 sensor kit (P907) has very small sensors because semi-quantitative measurement is adopted, the method is not commonly seen and many are not aware of the risks of obtained CO2 readings from the semi-quantitative CO2 kit sets, and to make matter worse, the semi-quantitative measurements are also being made used of to display a flawed continuous CO2 waveform.

 

Nihon Kohden cap-ONE P907 (TG-920P) mainstream CO2 sensor kit

How to remove a relatively big disposable adapter from the two tiny transducers after use?

 

When the sensors become smaller, it also means the disposable adapter becomes relatively much bigger as seen in this below picture. When trying to remove the disposable adapter from the transducers, it is difficult to separate the two because of the latching mechanism. A small size transducer means anything that latches onto it must be even smaller.

It is not easy to separate the disposable adapter from the Cap-ONE transducers after use

 

When removing disposable adapter from the mini sensors, users tend to just pull from the cables and this action quickly weakens the joint holding the sensors and cables. The action will cause stress to the two joints and quickly degenerate the performance of the transducers. This means the transducers are unlikely to last.

 

Users just doing the inevitable

 

Shown below is another TG-900P etCO2 kit set (order code P903) that makes semi-quantitative CO2 measurements on a traditional mainstream CO2 sensor. The TG-901T3 kit set (order code P906) is the same thing but using a non-coded connection plug. The medical devices from same manufacturer that make use of semi-quantitative CO2 kit sets for patient CO2 measurements and waveform include:

- Life Scope patient monitors

- Vismo patient monitors

- Cap-STAT OLG-2800

- CardioLife defibrillators

- Neurofax EEG machines etc.

 

Nihon Kohden semi-quantitative CO2 kit sets with traditional mainstream transducer

 

The manufacturer is not aware semi-quantitative CO2 measurements are only estimates

 

To save costs, the semi-quantitative kit sets do not make measurement during the inspiration phase. The important point is there is a measurement duty cycle and it is as shown; there is no way to know the actual CO2 measurements during the inspiration phase because CO2 measurements are not made.

Semi-quantitative means there is a duty cycle, and measurements are not continuous

 

Semi-quantitative measurement is also of low-accuracy type, performed using one IR detector instead of the usual two to save cost. This is reflected in the measurement tolerance.

 

Contrasting, quantitative measurement delivers high accuracy for critical care. To ensure the necessary high accuracy, quantitative measurement employed two IR detectors for simultaneous CO2 measurements at different wavelength for results comparison. CO2 measurements are also being made continuously.

 

Quantitative measurement employs two detectors to make continuous measurement at different wave-lengths to compare readings for high accuracy

NIHON KOHDEN specification for TG-901T CO2 sensor kit shows even the specified low accuracy of CO2 measurement using semi-quantitative method no longer holds true once CO2 is present during the inspiration phase.

This is because actual CO2 value will be more.

 

Semi-quantitative design cannot assure users the CO2 level is definitely zero during each inspiration phase!

 

Measurements are invalid when CO2 is present during inspiration, but the design does not measure CO2 level during this period!

 

As seen from the duty cycle, there is no measurement being made during the inspiration phase, how does the manufacturer assure measurement accuracy? The specified measurement tolerance is conditional and has no meaning for the users!

Each semi-quantitative CO2 measurement is in fact only an estimation.

In addition, since the users are not alerted on screen there is no CO2 measurement being made during the inspiration phase, they are unknowingly made to take on an unnecessary risk.

 

Semi-quantitative methodology means cost-effective estimations but the design cannot be used in a general way, only on a selective basis with known risks

 

For example, semi-quantitative methodology can be used as a simple estimation tool for obtaining the numerical value of End-tidal Carbon Dioxide level (etCO2).

 

Below picture shows the semi-quantitative method in the way it was intended for, estimating only the etCO2 numerical value for purpose of airway tube placement confirmation. It is not for continuous waveform display.

A hand-held semi-quantitative etCO2 estimation tool (with SpO2) for airway tube placement confirmation

The manufacturer ended up ignorantly displaying a flawed continuous CO2 waveform using semi-quantitative measurement kits that do not have ability to make continuous measurements

NIHON KOHDEN also allows data from semi-quantitative measurements to be displayed on screen with the non-measurement period reset to zero level. The insistence to display a continuous waveform using discontinuous measurement data from semi-quantitative mainstream CO2 estimation kits is unacceptable; the manufacturer is just subjecting the monitored patients and users to dangerous misinterpretation risks.

 

A zero CO2 reading on the waveform means zero measured value. No measurement can only mean a defective sensor, not by design!

Note the end tidal CO2 (etCO2) value shown is also not alerted as "estimated etCO2" only.

 

A flawed CO2 waveform with non-measurement intervals reflected as zero measured CO2 value

 

As seen from the two true CO2 traces below, expiratory upstrokes do not always start from zero CO2 level!

Quantitative measurements confirming expiratory upstrokes do not always start from zero CO2 level

  

Check the latest updated table to make sure you only use quantitative method for critical measurements and to display a true CO2 waveform on the screen.

 

Use only quantitative method for waveform display; the quantitative TG-950P (P905) shown here was already discontinued.

 

What you should know about fully-quantitative type miniaturized mainstream CO2 sensors

The TG-907P CO2 Sensor kit (order code P909) shown in above table is declared as using quantitative method. This sensor was designed for non-intubated adult CO2 monitoring, as well as neonatal CO2 monitoring. Nihon Kohden is thus offering an alternative to sidestream CO2 sampling methodology.

 

The miniaturized CO2 sensor is easily broken by the bigger and stronger adapter

 

In addition to the dead space problem, they had not foreseen miniaturized mainstream CO2 sensors could be easily broken by the disposable adapters. This happened because the disposable adapters are now relatively bigger and stronger!

These are common defects of a TG-970P CO2 sensor kit (P909). The design is impractical.

The fragile miniaturized CO2 sensor are clearly of poor design, and easily broken

The key point is, it does not last

 

 

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