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Messages - pfabsits

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1
Equipment and Software / Re: pH Meter on a Budget
« on: May 28, 2019, 11:01:45 PM »
After a not-so-good experience with a really cheap pH meter years ago, I went back to the ColorpHast strips and have to say I haven't had any regrets, but I'm starting to do some kettle sours and the 4-7 range doesn't cut it for that. Looking through some old threads it seems like the recommended models run about $120, which is hard to justify for home use.

Anyone have any experience with the Beverage Doctor? From what I've seen it's pretty new on the market: https://www.morebeer.com/view_product/43778

At $50 for ±0.01 readout and a replaceable electrode, it seems like a bargain.

There are many options available from Hanna Instruments. I would recommend getting a meter with ATC since the influence of temperature on pH increases as the pH goes down or up from 7. That is pH 7 is the isopotential point with regards to temp (changing temp does not change value).  If you are using for mash then I would still recommend some cooling. There are probes rated for high temperature but I would still stay under 170 oF.

https://hannainst.com/hi98107-phep-ph-tester.html

$39.95
Has ATC
Automatic 1 or 2 point calibration
pH/Temp readout
Waterproof

Cons:
ATC to 122 oF. It looks like the temperature reading will only read and compensate to 122 oF. I will have to confirm since we use 122 oF for meter environment which is nto the same as what a probe can be used for.

The HI98107 would be equivalent to our HI98127 with 0.1 resolution and replaceable probe. The meters with 0.01 resolution would include HI98108 and HI98128 (with replaceable probe). I like 0.01 pH resolution but realize most people are looking at 0.2- 0.3 pH unit accuracy since best practices are not used.

Our meters are made in our factory. We do not contract manufacture. That means design, electronics, injection molding, glass blowing, chemicals, etc are all done in house. The main factory is in Romania with our most expensive products (titrators, spectrophotmeters) made in Woonsocket, RI.

The testers that you see on Amazon are typically Chinese knock offs. Ours and our competitors designs have been copied and sold through various channels. In India someone would import then pad print our name with instruction manual. The testers that I have purchased from the local market did not work.

Bottom line: If you buy from us we are here for warranty and service support. If you have questions tyou can talk to an Applications Engineer. Most problems that we find are on the user error side. It is important to keep probe hydrated by using storage solution. It is important to periodically clean the electrode. It is important to calibrate with fresh buffer (Use sachets for the infrequent user).

I have posted a lot of information on pH. If you have any questions I am more than happy to help.

2
Equipment and Software / Re: Looking for opinions on a new PH probe
« on: March 15, 2019, 04:10:12 PM »
I looked at the Apera website and read the instruction manual

I cannot tell the glass type. They are rating for 100 oC so it might have HT glass. It looks like they add dye to the buffer in the indicating probe and that is why it is blue.

It is a glass body refillable with a double junction and has a bullet shape sensing tip.

It has a single junction design.

https://hannainst.com/hi1131b-refillable-combination-ph-electrode.html

The link to the HI1131B has the following specs
glass body
refillable
double junction
HT glass
single ceramic

It is the electrode that is supplied with all of our benchtop meters.

I will say one thing, We actually manufacture all of our own probes. That include the glass blowing. There are not many companies in the world that actually make pH electrodes. It is a true art form.


3
Equipment and Software / Re: Looking for opinions on a new PH probe
« on: March 15, 2019, 03:47:16 PM »
The Milwaukee meter uses a BNC connector for the probe. A BNC connector is a universal connector so any probe with a BNC can be used.

When deciding on a probe there are a few considerations that should be know before deciding
1) Temperature that you measure at. The rule of thumb is that a pH probe will last 1-2 years at 25 oC/78 oF. For every 25 oC increase the life is cut in half. So at 50 oC the probe wil last 6 months to 1 year, at 75 oC it will last 3 to 6 months and at 100 oC it will last less than 1 month.

To overcome there are different glass types. Most probes use general purpose (GP) glass. There is also high temperature (HT)  glass that is rated to 100 oC. The high temp is still brutal on the probe but the longevity will be increased. For a brewer that measures around 150 oF the HT glass is the best option to have.

2) Junction: Every pH electrode has a junction in which solution inside the probe leaks through to the sample being measured. This solution must be free flowing so there is continuity between the reference wire on the inside and the sample. Most probe use a small ceramic frit. This can become clogged is the sample has a high solids content. There are other junction types including PTFE, sleeve with ground glass and open junction. If it is for the wort then you should be okay with ceramic but if in the mash then a ground glass with sleeve would be a benefit.

3) Tip shape: The bulb can be round, flat, and bullet shaped. The round is a standard in the industry but can be a little more challenging to clean. A flat tip is easier.

4) Body type: The body of the electrode can be plastic, glass, or metal.  The plastic ones typically have plastic fins around the probe to guard from breakage. The challenge is then trying to clean since the fins get in the way. The metal body ones typically use a flat tip which allows for easy cleaning.

5) Refillable or gel filled: Refillable are nice since they can be periodically refilled with the reference solution. The fill cap has to be loosened when taking a measurement so the electrolyte will flow. The gel filled ones are maintenance free.

https://hannainst.com/beer-ph

The link above has an economy probe that is plastic body, polymer gel filled, GP glass, and single ceramic junction

After reviewing our electrodes I notice we do not have a HT glass version for plastic or titanium body. I will bring this up and hopefully will have that as an option for you in the furture.



4
Equipment and Software / Re: Ph reading confusion
« on: October 27, 2018, 05:58:59 PM »
I recently bought the Apera PH60 for testing my ph during the mash and have been noticing some discrepancies in my readings. Here was my most recent process:

1. Calibrate the ph reader
2. 5 min into mash I pull a small sample and put in freezer to cool
3. Once sample reaches 100 degrees I take a reading. This particular time I got 5.3
4. According the beer smith 3 calculator I add 1.6 ml of lactic acid and then stir the mash. I usually get the lactic acid in within 15 mins of starting the mash.
5. After 60 min mash I pull another small sample and cool.
6. After it reaches 100 degrees I test the sample. This time I get 5.33.

What am I doing wrong??? Why is my ph going up??? Any input would be greatly appreciated. Thanks!

A rise in 0.03 pH is insignificant. It is very difficult to obtain +/-0.01 pH. Many factors involved from probe condition (offset and slope), quality of buffers, to even the the temperature of the sample. A pH is to be reported at a specific temperature. A pH of a solution can very by temperature which is separate from the ATC that compensates for the temperature effect on the glass as according to the nernst equation.

On a separate note the influence of adding acid to a solution on the pH measurement is based on the alkalinity. If the water is low in alkalinity the greater the influence. If the water is higher in alkalinity (higher the buffering capacity) the less the influence. RO water has very low alkalinity while groundwater is typically high (especially) in the midwest.

To better understand fill two glasses with RO water. Add a teaspoon of baking soda to one glass. Measure the pH of each. Take an acid like vinegar and count the number of drops it takes to reach pH 4. You will find that the water without baking soda will take 2-3 drops. The one with baking soda will take a very large amount. You can add 100 ml (~1/2 cup) and still not go past pH 6. The reason being is that you increased the alkalinity with the baking soda and until all of the bicarbonate is used up the solution will be buffered against the acid.

HCO3- + H+ --> H2CO3 --> H20 + CO2

5
Equipment and Software / Re: Ph Meter and Bru’n Water
« on: April 18, 2018, 08:33:26 PM »
1) It is important to note that the pH of a solution is affected by temperature. This affect is not typically compensated for by a pH meter.

2) pH meters with temperature compensation will compensate for changes in the membrane potential (sensing glass) according to the Nernst equation. The Nernst equation is the basis for pH measurement with membrane (glass) electrodes.

This compensation is the reason that a pH meter will show a different reading right after calibration. The displayed reading is the actual pH of the solution at a given temperature (#1). The buffer solutions have known values for pH vs. temperature. For example at 59 oF (15 oC) the pH of 7.01 buffer is pH 7.04 and not pH 7.01.

According to the Nernst equation (#2) a pH electrode will generate 59.16 mV/pH unit (slope) from pH 7.0 at 25 oC. At pH 7.0 the mV is theoretically 0 mV while a pH 6.0 is +59.16 mV. At 15 oC the response is approx. 54 mV/pH. ATC compensates for this change in slope.

When a pH reading is taken it is important to note the temperature of the sample because this is the pH of that solution at a given temperature (#1). The same solution can have a different value at a different temperature.

There are other factors that affect pH measurement including conductivity of the water, activity of the ions, condition of the probe (offset/slope), an the list goes on. Overall I would say that if you are within 0.1-0.2 pH of the expected value then you are doing pretty good. To achieve accuracy of 0.01- 0.05 pH is very challenging and would require decent knowledge of pH measurement and best practices.

Basics would be
1) Offset +/- 25 mV
2) Slope 92-105% (54 - 62 mV/pH)
3) Having a clean electrode
4) Having a clean and free flowing junction
5) Using fresh buffers. Ph calibration is only as good as the buffer being used
6) Properly hydrated probe (stored in storage solution for at least 304 hours before use)
7) Use two beakers for each buffer and sample. One beaker to rinse and one to test.
8 Conductivity of solution of at least 100 uS/cm
9) For mash use High Temperature (HT) glass. As temp goes up resistance of the glass goes down. With Ohm's law V =IR the V (voltage) is fixed by Nernst so affecting R (resistance) will also affect I (impedance).  There is an ideal amount of impedance (current) for the meter to measure properly.


6
Equipment and Software / Re: ATC help with new meter
« on: February 20, 2017, 05:06:05 PM »
ATC corrects for the Nerstian response for a membrane potential (i.e. pH electrode). Temperature is a factor in the Nernst equation. At 25 oC a pH electrode theoretically generates 0 mV at pH 7.01 and +177.48 mV in pH 4.01. The pH 4.01 value represent 59.16 mV/pH unit and since pH 4.01 is 3 pH units away the theoretical voltage is 59.16 x 3 @ 25 oC.

pH 7 is known as the isopotential (iso = same) point in which Theoretically it should always be 0 mV. For the pH 4.01 value (or slope) the mV/pH will change with temperature. For example, 54 mV/pH unit at 0 oC and 64 mV/pH at 50 oC. Again, these values are calculated by changing the temperature value in the Nernst equation.

pH meters with ATC use the Nernst equation to correct for temperature variations as predicted by the Nernst equation.

It is critical to note that the values on the bottles/packets of pH buffer solutions are the pH of the solution at that specific temperature. It is the reason why some meters will display a different pH value after calibration. The meter is programmed to display the solution pH buffer value for for the temperature being measured. The pH at any given temperature for a NIST traceable buffer is 100% known while the pH of wort at 25 oC versus 50 oC is not known. The actual wort pH can be different at different temperatures. It cannot be predicted with 100% certainty since the composition is never 100% exactly the same.  So for a pH meter we program what we know.  This is not the same as ATC. ATC does not correct for solution pH but for the Nernstian behavior.

Temperature does impact the resistance of the glass membrane. As temperature goes up the resistance goes down. It is one of the main concerns when measuring at very high temperatures. Ohm's law stated that V = IR. (V=voltage, I = impedance, R = resistance). The voltage is predicted by Nernst and R is the resistance of the glass membrane (around 100 megaohms for general purpose glass at 25 oC). With voltage staying the same and resistance decreasing then the impedance is affected, which has to be within an ideal range for a pH meter to work correctly. It is recommended to use pH electrodes with high temperature (HT) glass for measuring above 150 oF.

Bottom line:
1) ATC will correct the slope based on the temperature of solutions used for calibration.
2) With ATC, most meters will display the solution pH (the value printed on the bottle)
3) For Manual Temp Compensation (MTC), measure the temperature of the buffer and adjust meter pH value to match the pH value for given temperature from the table printed on the bottle.


7
Equipment and Software / Re: pH probes
« on: February 20, 2017, 03:34:17 PM »
Any pH probe with either BNC or DIN connectors can be replaced with any other manufacturer's BNC or DIN equipped probes. They are universal.

You can get my compilation of pH meter and probe advice on the Bru'n Water Facebook page linked below. You'll have to scroll through a bunch of other useful brewing related information to get to that pH info, but it should be worth your time.

The BNC connector is universal but the DIN most likely will not be.

For Hanna Instruments pH/Temperature probes, the current selection with DIN connectors, are proprietary. In the wiring are two wires for powering an amplifier circuit built in the probe. The amplifier takes the voltage produced by the pH half cells and allows for more current to flow to the meter. The advantage of an amplified circuit is reduce noise from (pumps, motors, lamps, etc) and humidity. We include the amplifier with sensors that have a built-in thermistor temperature sensor since the noise from the temperature measuring circuit can interfere with the pH measurement.

We have some probes with DIN connectors that were used in the past without temperature or amplifier. They are not used by any meter that we currently produce. I think they are a left over from a European standard that was used in the past. I am not aware of any current manufactures that they would be compatible with. They are not the same DIN as the ones used by Hach (digital signal), Thermo, WTW, etc.

On a side note: It was the amplifier circuit that made pH measurement possible. Arnold Beckman used a vacuum tube type amplifier to build the first pH meter for his friend Glen Joseph with the California Citrus Growers Assoc. At one time Arnold Beckman worked for Tellabs (Ma Bell) in which it was important to amplify the telephone phone signal. Below is a link to an ACS publication about Arnold Beckman and the pH meter.


https://www.acs.org/content/dam/acsorg/education/whatischemistry/landmarks/beckman/beckman-ph-meter-commemorative-booklet.pdf

8
Equipment and Software / Re: pH probes
« on: February 07, 2017, 08:50:49 PM »
Phewwww. That is a ton of good information there. Thanks for sharing.

In your first post with steps 1-4, can this be performed with any pH probe or just Hanna Instrument ones?

The offset check (pH 7.01) will work with any meter with a BNC connector. Once the connector is shorted then a o mV signal is being sent to the meter.

Many meters, including testers, that have automatic calibration have the ability to clear the calibration data that has been stored.  A meter with a default calibration will be set to 0 mV = pH 7.01 and +178 mV = pH 4.01. From a default calibration it is then possible to determine both offset and slope.

The original post was for a meter that was calibrated manually. Since it has a BNC connector it was at least possible to check the offset. The slope would be difficult to check since a +178 mV signal from a simulator would have to be driven to the meter to adjust the pH 4 trimmer. Since more than likely a simulator is not available that the slope check was left out.

The offset is very helpful since a high offset value is an indicator that the probe needs to be cleaned. 

If you have a meter with auto calibration and it can be cleared to a default then knowing the readings in buffers will allow to calculate both offset and slope.

Feel free to message me and I can walk you through how perform the calculation. It is based on the Nernst equation in which theoretically a pH of 7.01 is 0 mV and each pH unit generate 59.16 mV at 25 oC. Acids the pH increases positive and bases the increase is negative. A pH electrode with 100% slope will generate +59 mV in pH 6 while in pH 5 will generate +118 mV.  It would be recommended to make sure that the probe has better than 90% slope or 54 mV/pH.

For example, on default calibration my pH probe reads pH 7.25 in pH 7.01 buffer and pH 4.5 in in pH 4.01 buffer.
*pH 7.25 is 1/4 pH unit away on the base side so the voltage being generated is -15 mV. Well within +/-30 mV for an offset.

* pH 4.5 is 2.5 pH units away from pH 7.00 which in mV that would equal 59 * 2.5 = 147.5 mV. But since the offset is -15 mV then the mV difference is 147.5 - (-15) = 162.5 mV. 162.5/178 x 100 = 91.3% slope.  The slope is above 90%.

* If in the same example the pH meter read pH 6.75 in pH 7 for a default cal then the voltage would be +15 mV (more H+ = increase in + voltage). The slope would be 147.5 - 15 mV = 132.5 mV. 132.5/178 x 100 = 74.4% slope. Most meters will not calibrate less than 85% slope but if it did then you definitely should not use the probe since the slope is too low.

The numbers above are approximate since Nernst dictates 59.16 mV/pH at 25 oC. I have rounded to 59 for convenience. Either way, knowing how to approximate the offset and slope will help you understand the health of the pH electrode. To achieve an accuracy >0.1 pH it is critical to know.

The accuracy statement of the meters stated by the manufacturers is the meter itself and not the system which includes the probe. I can achieve a higher accuracy from a $50 tester than from a $600-1K benchtop if the probe of the tester has a good offset/slope and the benchtop does not.

General rule:
New pH electrodes: +/- 10 mV offset and 95-105% slope
User tolerance: +/- 30 mV offset and slope greater than 90%
Meter limits: +/- 60 mV offset and slope greater than 85%

It is possible to calibrate a probe that is outside the limits of use since the window for calibration is pretty wide. At that point it is like throwing darts and were hitting the dart board. To hit a triple 20 you want to be well within the user tolerance range.

9
Equipment and Software / Re: pH probes
« on: February 06, 2017, 07:00:26 PM »
So when do you guys take your ph readings? If its at the 15 min mark in the mash do you draw a sample and let it cool before reading with your meter? I noticed the thermoworks model im looking at says it has temperature compensation built in.
The temp compensation is to accommodate the different ph at different temps and not to adjust the reading to what it would be at room temp.

I pull a small sample at 10 minutes and put it in the freezer for about 10 minutes to test.

Thanks Steve
Any opinions on the thermowoks stuff? Thermometers are stellar.

I cannot state for Thermoworks but as far as temperature goes:

Most pH electrodes are made of General Purpose (GP) glass. The rule of thumb for GP glass is
At 25 oC expect 1-2 years
At 50 oC expect 6 month to 1 year
At 75 oC expect 3-6 months
At 100 oC expect less than 1 month.

The guidelines are for probes in continuous use. I would expect a longer time for probes that are used intermittently.

It would be recommended to cool samples to less than 140 oF (60 oC). If it is planned to measure at a higher temperature then a pH electrode with high temperature (HT) glass would be recommended. The HT glass has a higher resistance at 25 oC than GP glass. As the temperature increases then resistance decreases. The HT glass resistance at high temperature approaches that of GP glass at an ambient temperature.

The temperature compensation is used for voltage response as according to the Nernst equation for membrane potentials.  For a meter with manual temperature compensation it is important to adjust the calibration trimmer to match the value on the bottle at a specific temperature. The value on the bottle is the actual pH of that solution at a given temperature. For example pH 7.01 and 4.01 at 25oC.

10
Equipment and Software / Re: pH probes
« on: February 06, 2017, 06:44:13 PM »
On average we state that a pH electrode will last 1-2 years. It is very possible to have a probe work longer. As long a pH electrode has a good offset (mV value in pH 7.01) and slope (mV difference from pH 4- pH 7) then the probe can be used.

A good offset value is +/- 30 mV while slope should be greater than 160 mV (90%).

Since the meter is calibrated manually and it does not have a GLP feature it can be difficult to determine the pH electrode characteristic. I would recommend the following:

1)   Short the BNC connector on the meter with a paperclip. That is put one end in the center hole and touch the outside of the connector.  This is 0 mV.
2)   Dial pH 7.01 calibration trimmer until pH 7.01 is displayed
3)   Reconnect the pH electrode to the meter and place in pH 7.01 fresh buffer
4)   Record the pH value in the buffer.

It is now possible to determine the offset of the pH electrode. Ideally the meter would display pH 7.01 since the theoretical mV at pH 7.01 is 0 mV at 25 oC. An acceptable offset of +/-30 mV would be displayed as a pH from 6.5 to 7.5. Meters will typically allow a calibration of +/- 60 mV which would show as a pH reading around 6 (+60 mV)  and 8 (-60 mV).

If you see reading outside pH 6.5 to 7.5 then the electrode needs to be cleaned. Any coating on the glass will shift the voltage read by the probe.

Instability in readings that occurs with aging are due to various factors including:
1)   Dirty electrode – as there is a build up on the glass the measurement circuit is impeded.
2)   Clogged junction – on the side of the probe should be a white plug. That is the junction. When it gets clogged the measurement circuit gets impeded.
3)   Storage -  It is very important to store the pH electrode in storage solution. The storage solution maintains a hydrated layer on the glass bulb, hydration of the junction, and hydration of the gel used inside the probe.


Below is a link to some basic maintenance information:
http://hannainst.com/ph-electrode-maintenance-calibration-guide

Products for Beer Analysis.
http://hannainst.com/beer-ph

Recommended cleaning solutions
http://hannainst.com/industries/beer/ph/maintenance-solutions/cleaning.html

If you have any questions then feel free to message me.

11
Equipment and Software / Re: Cheapo pH Meter Experience
« on: January 13, 2017, 05:04:23 PM »
The link provided to the Hanna product was for a 0.1 pH resolution. We do have the exact same meter with a 0.01 pH resolution for $10.00 more.

http://hannainst.com/hi98108-phep-ph-tester.html

It is important to note that unless you monitor the offset and slope of the pH electrode it is difficult to obtain a high accuracy reading that is better than 0.1 pH units.  I have been with my company for over 17 years and have worked with pH in pretty much every industry and with every format (pockets to process control).

Just because a pH meter reads pH 7.01 in a buffer after being calibrated does not mean that it will read the sample accurately. I have seen greater than a 0.5 pH unit difference between two probes in the same sample even though they read the same value in the buffers.  The reading I trust is based on the offset and slope. That is in pH 7.01 the probe needs to be +/- 30 mV and the slope (mV change from pH 7 to 4) greater than 90%. Manufacturers program the meters to accept +/- 60 mV or greater in pH 7.0 and a slope of at least 85%.

Below is a link to basic tips on pH electrode maintenance.
http://hannainst.com/ph-electrode-maintenance-calibration-guide

The electrode characteristic is very important. Our QC tolerance in manufacturing is +/- 10 mV in pH 7 and a slope greater than 95%. This is the area that is the biggest difference between companies like Hanna, Mettler, Metrohm, Hamilton and other reputable companies and the knock offs.

To truly understand in there is a difference between a $13.00 meter and a $50 one it would be critical to understand the electrode characteristic. The biggest challenge for a manufacturer is with the sensor. It is the most important part of the measuring system.

Personally, I prefer a 0.01 pH resolution but for the number to be meaningful would require a knowledge of pH electrodes and the behavior in the buffers. For the brewer measuring a pH less than 5.6 at 140-150 <sup>o</sup>F it would be more important to have ATC than the increased resolution due to the effect temperature has on the membrane potential.

Unfortunately, I cannot figure out to attach an article that was written for a publication that was based on the Orange County Water Department problem with pH readings that were 1 pH unit apart from a field meter versus a lab meter.  The problem was with a 60 mV offset (fixed by simple cleaning) and a low slope due to their pH 10 buffer actually being pH 9.5. If anybody is interested then just message and I will forward.

12
Equipment and Software / Re: Cheapo pH Meter Experience
« on: January 10, 2017, 09:17:13 PM »
All pH meters have a reference junction. When a new meter is received most likely both the pH sensing bulb and the junction need to be hydrated. A meter shoudl be placed in storage solution or a pH buffer for at least 3-4 hours before use.

It is common to see the pH calibration change if the probe is not hydrated. The reason being is that calibration is compensating changes to the sensor. So a dry sensor has one characteristic as compared to a hydrated one. If the probe is calibrated when it is dry and then allowed to hydrate, the meter will no longer be calibrated. Seeing a 0.5 pH change as the hydration process occurs over time is not unusual.

The drying of the junction was most likely the cause of the sluggish response and instability issue. The junction is an electrical pathway from the internal reference to the sample. If dried out or clogged then current cannot pass and the result is erratic readings.

The vast majority of pH meters available are using pH electrodes with a Ag/AgCl reference. That is one of the wires in the pH electrode is coated with a silver chloride coating and then placed in a solution saturated with silver. A reaction occurs that produces a stable potential as part of the measuring circuit. Even though we still make pH electrodes with Hg/HgCl reference, they are not typically used due to the handling of mercury. In R&D the Hg/HgCl reference is used as a benchmark when testing new designs.

My guess the reason that the research grade benchtop held its calibration is that the probe was hydrated, calibrated and stored properly. I have had testers sitting in a instrument case for 6-12 months and pull them out to see that they are holding their calibration.

The $13.00 price is appealing for a pH meter but there should be many other considerations when choosing a pH meter than just price. For example, local warranty, support, and that the products are QC by the seller and not just passed along through a distribution channel. For the more advanced brewer that is investing in portable and bench meters then it becomes more important to understand the choices in sensors available including a sensor that can withstand high temperatures.

For the user on a fixed budget, we have just launched a new meter at $39.50. Has all the bells and whistles including battery percent level, stability indicators, temperature readout and automatic calibration. The feature that I like best is the extractable junction since if it gets clogged (i.e. solids in mash) then it can be cleared making work like new again. 

http://hannainst.com/hi98107-phep-ph-tester.html


Before Hanna, these testers did not exist. We are the one that brought the technology to market in 1986 and have been improving it ever since.

13
Equipment and Software / Re: pH meter calibration
« on: November 18, 2016, 12:29:52 PM »
With pH calibration there are two very different issues that occur with regards to temperature.

1) The science behind the measurement is based on the Nernst equation which is for membrane potentials. The equation is temperature dependent in which a value must be used.

2) The pH of the buffer solution is temperature dependent. That is a pH 7.01 buffer is pH 7.01 at 25 oC. At 20 oC the pH of the solution is pH 7.03.

A meter with ATC will correct for the Nernst equation. The Nernst equation (when all values are plugged in) dictates that there will be 59.16 mV/pH unit at 25 oC. The mV/pH will change with temperature and we correct for this.

The pH of the solution is not compensated and it is for this reason that pH is reported with a temperature value. For example my Mash is pH5.5 at 50 oC. The actual pH of the mash can be different at different temperatures. We do not know to what extent since the composition changes. Unlike a pH buffer based on NIST standards in which the actual pH values are known at different temperatures.

For Hanna meters with automatic calibration it is the reason that the meter displays a different value from the pH value after calibration. For example I calibrate in pH 7.01 buffer at 20 oC. After calibration the meter will display pH 7.03. That is the pH of the solution that we know for 100%.

For meters with manual calibration adjust the pH value to match the value on the tables found on the bottles of buffer with regards to temperature. That is a best practice.

I hope this helps. If not feel free to message me with any questions.


14
Equipment and Software / Re: pH monitor
« on: November 18, 2016, 12:13:53 PM »
As an employee of Hanna I would like to point out a couple things from the comments above.

Our pH Checkers (HI98103 and HI98100) currently have an open junction design for the pH electrode. The open junction helps to prevent any clogging from solids found in a sample. It is important to note that the open junction design uses an agar based electrolyte. An agar is like jello in that it is liquid when hot and a gel when cold. For this reason it is important to not use above 50 oC/ 122 oF. Also being an open junction means that it is susceptible to drying out so it is important to add a couple drops of storage solution to the protective cap when not in use.

On a side note, I have displayed the Checkers at tradeshows for many years and it is amazing that they can sit in a storage case and when taken out they always work. I typically place in coca cola to engage with the people with a sense of curiosity to its pH. A lot of people do not realize how acidic a cola is.

The HI98100 is a new version of the HI98103 and added a bunch of new features including automatic calibration.

The second thought was with the pHep 4 (HI98127) which is the same as the pHep 5 (HI98128). They are only different in resolution.

The pHep 4 has an extractable junction for the pH electrode. When looking at the glass a small piece of cloth can be seen on the side. What this junction does is allow the user to pull a small portion out so that any clogging that occurs can be cleared. When a junction becomes clogged the readings will tend to drift and/or be erratic. This will present a problem with not only getting a stable reading but also with calibration. Meters that have automatic calibration look for stability. If the reading is not stable then the meter will not accept the pH value of the buffer. When this happens simply pull a small portion of the junction and the response and stability behaves like a new probe.

It is important to only pull a small portion (1/8"). The junction is only 1.5-2" long so it can be completely pulled out. So just a little needs to be pulled out.

As a side note: the pH junction is a barrier from an internal wire inside the probe and the solution to be measured. The electrical pathway must be clear for any pH meter to work properly.

If anyone ever has any questions about pH or other analytical equipment then please feel free to message me.

We also have Technical Sales and Application Engineers on staff for support. They are always available at 877MYHANNA (694-2662).

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Equipment and Software / Re: More User Friendly pH Meter
« on: September 12, 2016, 03:33:07 PM »
Is there a more user friendly (i.e. moron proof) pH meter out there?  I seem to not be that good at calibrating and getting good readings.

Currently use a MW102.

I am to sure if you will find an easier to use meter.  The MW102 has automatic calibration which will present problems when the probe need to be cleaned or changed. Being auto-calibration, the meter will be looking for a specific voltage window for offset (pH 7.01 calibration) and for slope (Change from pH 7 to pH 4). If the right voltage is not generated then the meter will not calibrate. In a way this is a good thing since if the probe is too far out of specification then it should not be used. A qucik way to check is to pull the battery from the meter to clear the calibration. The place the probe in pH 7 buffer. If the value is below pH 6 or above pH 8 then the meter will not calibrate since the offset is greater than 60 mV (1 pH unit). At that point you can try cleaning the probe to see if it is the cause of the offset error.

Another challenge with automatic calibration is that the meter looks for stability before locking on the reading and allowing you to confirm the value. If the reading is drifting and there is no stability then the "cfm" will not be displayed.

Drifting readings are a sing of a dirty electrode or clogged junction.

Those are the main problems for meters with automatic calibration. It is possible to buy a meter with manual calibration in which there are trimmers used to adjust pH 7 and pH 4/10 buffers. They do not rely on stability but will have the same limitation in offset/slope acceptance. That is if on a default cal (short BNC connector to adjust to 7.0) the pH reading of the probe in buffer will still only allow +/-1 pH unit. So any reading of the pH probe in pH 7 buffer greater than pH 8 or less than 6 will not be adjusted to pH 7.0. There is not enough span to do so.

A couple of final points:
* pH electrodes last about 1-2 years. If you can check offset and slope then the probe can be used as long as the offset +/- 30 mV and slope >90%. Meters calibrate to +/- 60 mV and slope >85%.

* When not using the probe store it in storage solution. If you do not have storage solution then use pH 4. Lower pH's inhibit microbial growth.

* Rinse the electrode with purified water before calibration, before use, and after use. Aquafina is purified by RO so it is pretty clean. Other bottled water can be purified by RO but some companies add minerals back in for taste. I would not use this water for rinsing the electrode. Distilled water is also available at the local grocery store.

* Use fresh buffers. If you only use the meter periodically (i.e. 1/week, 1/month)then use buffers in packets. Use the packet once and dispose. If using daily then a jar can be used for calibration buffer that is replaced every 3-4 days with fresh solution. Never pour pH buffer back into the bottle that it is supplied with.


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