FAQs
Sensors: How long can Polestar sensors be stored?
The lifetime of the sensors is mostly dictated by the loss of indicator due to photobleaching. If stored in the dark our DO sensors will last for at least 3 years and our pH sensors for at least 2 years without detectable loss of sensitivity or accuracy.
Sensors: How long will Polestar sensors last?
When properly cared for, pH and O2 sensors should last for at least 4 million measurements. At 30 second measurements, that is over 3 years of continuous use. You can use the AGC readings to monitor the usable life remaining in the sensor.
Sensors: What is the impact of ambient light on sensor performance?
The signal processing electronics and algorithms of Polestar's systems are designed to eliminate all frequencies of light but those frequencies associated with the fluorescence measurements. Ambient room light and sunlight do not affect readings, but will impact the lifetime of the sensor by contributing to photobleaching. Care should be taken to minimize ambient light exposure whenever possible.
Sensors: How does fluorescence in the process media affect Polestar sensors?
Fluorescent molecules in the process media can affect the readings from Polestar's pH sensor if the molecules exhibit fluorescence excitation and emission properties that are similar to those of the pH indicator the pH sensing film.
Sensors: Peel and Stick: Are all the types of plastic suitable for being used as the sensor support (for a peel and stick sensor)? Can we stick the patch on all types of glass/plastics without creating an interference with the light (the plastic will be between the sensor and the optic fiber)?
The glass/plastic should not exhibit fluorescence and must be sufficiently transparent to allow adequate transmission of the excitation and emission light signals to pass as demonstrated by the AGC and RAGC levels observed during a measurement. AGC and RAGC levels greater then 2500 indicate insufficient signal transmission for the measurement.
Material Certifications: Does Polestar have certifications for your sensors and probes?
Our sensing materials are USP Class VI certified and have passed the 87 and 661 tests. Our certifications are on our website. The stainless steel in the probe is 316L grade that is electropolished and passivated to industry standards. We keep those certification documents on file.
Calibration: Do we need to perform a single or multi-point calibration post SIP or is the calibration factor for a new probe sufficient?
All of our sensors are factory calibrated, however one- and two-point calibration routines are available with the DSP3000 and DSP4000 optical monitors. A standard steam in place procedure should not cause the sensor to require another calibration. However, you can perform a calibration if desired.
Calibration: Can sodium bisulfite solution be used for calibration of the O2 sensor?
It is possible to use sodium bisulfite solution as part of the unit's two-point calibration procedure, but not in the one-point calibration scheme. Our one-point calibration requires the value be non-zero. The calibration value is adjustable to the value that the sensor is seeing at the time.
Calibration: If a sensor comes calibrated, do I still need to do a one point calibration on it?
No. The sensor should be accurate and stable as delivered. However, you might achieve even greater accuracy by doing a one point calibration.
Calibration: Can the user buy a new sensor, not go to the Polestar website to download the calibration factor for the new sensor, but, instead, just do a one point calibration and then use the sensor?
Yes. However, the accuracy may not be quite as good as it would be with the Polestar provided calibration factors. Ideally, you would download and apply the calibration factor and then you would still have the option to do a one point calibration.
Calibration: Is recalibration after gamma irradiation or autoclave required?
Yes, after gamma irradiation, but not after autoclave.
Calibration: If post-sterilization calibration is required, how should it be performed (how many points, between 0 and 30%?)
For gamma irradiation of iDOTs, the sensors will be installed in the disposable bags and gamma irradiated along with a few calibration iDOTs from the same sensor batch. The calibration iDOTs are then calibrated at Polestar and the calibration files are put on the Polestar website. The customer can download the calibration files onto the USB in the DSP and boot up the system. The sensor films are processed in sheet form with one sheet of sensor film capable of producing hundreds of sensors that will all have the same calibration factor. Large quantity orders of bags can be made from the same lot of film to ensure the same calibration factors for the complete order.
Calibration: Do we need to recalibrate after Steam in Place?
You should not have to recalibrate after autoclave but we have limited data on the effects of SIP on calibration. Our suggestion would be to try it with and without recalibrating to see how it works under your specific conditions.
Gamma Sterilization: Under which conditions can the sensor be gamma irradiated? (Dry / in a buffer/in an atmosphere without O2? Are any special lighting conditions required?)
Sensors can be irradiated dry. We have not studied the effect of reduced/absent O2 during gamma irradiation. No special lighting conditions are required for gamma. However, as these are light sensitive films, standard precautions should be followed in order to minimize exposure to light and therefore extend the life of the film.
CO2 Measurements: Our fermentors are run at neutral pH (~7). Would that mean a majority of dissolved CO2 would be converted to bicarbonate? Does the probe detect the remaining molecular CO2 or the bicarbonate, or both?
Polestar's CO2 sensor measures only CO2, not bicarbonate. The pH dependent equilibrium that you are thinking of is for carbonic acid (hydrated CO2) and bicarbonate. Since the hydration equilibrium constant for CO2 at room temperature is 1.7E-3, nearly all of the CO2 in a system is present as CO2 not carbonic acid or bicarbonate.
CO2 Measurements: What is the response time of the CO2 probe?
The t90 response time of the CO2 sensor is less than 90 sec. That compares favorably with competitive technologies.
CO2 Measurements: When we calibrate at 5%, the DSP reads fine in and around 5%. But when we put probe in air it then reads 0.0% UR, why?
The level of CO2 in air is only 0.03%, below the detection level of the sensor.
Drift: What is the drift (before and after the sterilization)?
On the general issue of drift, we have studied it extensively before and after sterilization and continue to do so. Under controlled conditions we find very little drift over hundreds of thousands of measurements. For example, in head to head controlled comparisons with standard glass electrodes, our pH sensors perform as well as, or better, in tests lasting up to 500,000 measurements.
Drift: What are the reasons for drift in the sensor's signal?
The greatest sources of drift would be instrument warm up and, in the case of pH sensor, sensing membrane hydration. The DSP transmitters perform best when allowed two to three hours to warm up. The units are best left under power when not in use to maintain the internal temperature. The pH sensor, if it has been stored dry, should be hydrated for 30 min. Sensor element degradation and photobleaching can also lead to drift, but this occurs very slowly under normal operating conditions.
Media: We regulate our pH media by addition of NaOH, could this addition damage the sensor?
Addition of NaOH has no effect of the performance of Polestar's sensors.
Media: Will heavy aeration have an impact on the readings?
Heavy aeration or sparging should not affect Polestar's measurements of pH, O2 or CO2.
Temperature: Does temperature have an effect on sensor readings?
Yes. The temperature should be provided to the DSP when measuring O2 or CO2 but is not required for pH. Temperature can be provided manually through the operating system, or continuously through 4-20mA or an RTD. The DSP will automatically make the necessary compensation once the temperature is provided.
Temperature: On the temperature end of the menu what is the hibernate temperature selection?
The hibernate mode allows you to set a temperature above which the DSP will not sample the fluorescent sensor but will take temperature measurements. This option should only be used when temperature is automatically provided as with an RTD. The hibernate mode can be used during high temperature operations such as steam in place or autoclave. Once the temperature drops back below the hibernate temperature, the DSP will automatically begin sampling the sensor. The hibernate option prevents bleaching of the sensor when readings are not needed. (see DSP Manual under Set Hibernation Temp.)
Optical Cable: How long can a fiber optic cable be?
A fiber optic cable can function well up to about 10 meters. After that, the optical signal is degraded.
Optical Cable: What happens to the signal when the fiber cable is bent?
Bending optical cables reduces the signal carrying capacity of the cable but does not affect the measurements made with Polestar's sensors. A minimum bend radius of 1.5 inches is recommended to avoid damaging the fiber optic.
Data Management: Is it possible to log the data to the USB stick and, if so, how many data points can the stick hold?
Yes you can store data on the USB stick in the DSP in two ways. First, you can save the data to the USB stick from the main menu using the "Save log file" option. Also, as you turn off the DSP from the main menu, a menu option will appear that asks if you want to save the data on the USB. Answer "yes" by pressing the enter key. The USB stick holds 1 GB of data. If you take a measurement once every two seconds you can store approximately 6 months of data. If you need to store more data, you can use another USB stick with more capacity. Simply copy our files from the USB stick provided to the new stick and use that to boot the DSP and later to store the data. Make sure not to remove the USD stick during the run mode of the DSP.
Data Management: When we save data to the USB, does it over write the old files or does it create a new file on USB without losing old files?
If you select the option to create a new file when shutting down the DSP through the menu system, then, yes, it creates a new file each time. We recommend that you enter the time and date when you start up the DSP. That will assist in manipulating the data file when you save it later. Also, there is a utility program on the USB to assist in renaming the data file once it is created.
