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Page 35

12.6.3

 

Temperature Compensation

The slope of a pH electrode (section 12.6.2) is affected by temperature. This
effect is compensated for either by using an Automatic Temperature
Compensation (ATC) probe or by entering the sample temperature manually.
Figure 12-3 shows the slope of a pH electrode at various temperatures.

-600

-400

-200

0

200

400

600

0

7

14

Electrode
Potential (mV) at
0 oC (54mV/pH)

Electrode
Potential (mV) at
50 oC (64mV/pH)

Electrode
Potential (mV) at
100 oC (74mV/pH)

pH Electrode Response, as a Function of Temperature

Electrode Response (mV)

pH

Figure 12-3

12.7 Checking the reference junction of a pH electrode.

If pH readings are inaccurate or unstable, the reference junction of the electrode
may be blocked. The following test can be performed to determine if the
reference junction of a pH electrode is making adequate contact with the sample
solution.

1.

 

Calibrate the 

MC-81

, as per section 5.1.

2.

 

Dilute 1 part of pH6.88 buffer with 9 parts of distilled water.

3.

 

Measure the pH of the diluted buffer. The result should be 7.06 +/-0.05 pH.

4.

 

If the value obtained is outside of these limits, then clean the reference
junction, as per the instructions supplied with the pH electrode.

5.

 

Re-calibrate the 

MC-81

 and repeat the test.

6.

 

If the value obtained is still outside 7.06 +/-0.05 pH, then the electrode should
be replaced.

Summary of Contents for MC-81

Page 1: ...tion has a diagram and explanation of the display and controls of the MC 81 It also contains a full listing of all of the items that you should have received with your MC 81 Please take the time to read this section as it explains some of items that are mentioned in subsequent sections 3 Main Section The main section of the handbook provides complete details of the MC 81 including operating modes ...

Page 2: ...emperature Calibration 14 6 2 Calibration Notes 14 6 3 Calibration Messages 15 6 4 Manual Temperature Setting 15 7 BATTERY SAVER FUNCTION 16 8 SELECTING BUFFERS FOR AUTO BUFFER RECOGNITION 17 9 INITIALISING THE MC 81 18 10 TROUBLESHOOTING 19 10 1 General Error Messages 19 10 2 Conductivity and Salinity Troubleshooting 20 10 3 pH and mV Troubleshooting 22 10 4 Temperature Troubleshooting 23 11 WARR...

Page 3: ...Page 2 1 Introduction 1 1 MC 81 Display and Controls ...

Page 4: ...ee section 6 4 Also used to select buffers for automatic buffer recognition See section 8 Press to change modes between Conductivity Salinity pH and Temperature Press and hold down this key for 2 seconds to toggle between Conductivity and Salinity modes See section 2 2 Press to switch the MC 81 on and off Press and hold down this key for 3 seconds to invoke the Battery Saver mode See section 7 and...

Page 5: ...2201 4 pH6 88 Buffer 200mL 121306 5 pH4 00 Buffer 200mL 121381 6 2 76mS cm Conductivity Standard 200mL 122306 7 2ppK TDS Standard 200mL 122307 8 9V Battery 130026 9 MC 81 Handbook 130050 Options that may have been ordered with your MC 81 1 k 10 ATC Temperature Electrode plastic body 122220 2 36ppK Salinity Standard 1L 122304 3 Low volume k 1 ATC Temp sensor glass body 122216 4 NiCad Rechargeable b...

Page 6: ... Offset Range 10 0o C to 10 0o C Temperature Compensation pH 0 to 120 0 o C automatic or manual Cond 0 to 50 0 o C automatic only Auto Standard Recognition pH pH4 00 pH6 88 or 7 00 pH9 23 Cond k 1 cell 2 76mS cm k 10 cell 2 8mS cm 58 0mS cm Salinity k 1 cell 2 00ppK k 10 cell 2 0 ppK 36 0ppK Display 16 Character alphanumeric LCD with full text prompts and error messages Power 9V Alkaline Battery f...

Page 7: ...sly eg 2 76mS or 2 00 ppK 7 00 pH 7 00 pH Press and HOLD the key for 3 seconds to alternate between Conductivity and Salinity readout in this mode The Large Display format is not available from this mode Calibration is not available from this mode 2 Conductivity Salinity Temperature Displays Conductivity or Salinity and Temperature readings simultaneously eg 2 76mS or 2 00 ppK 25 0o C 25 0o C Pres...

Page 8: ...adout modes are 1 Conductivity Salinity Displays just the Conductivity or Salinity reading in large digits Press and HOLD the key for 3 seconds to alternate between Conductivity and Salinity readout in this mode 2 pH Displays just the pH reading in large digits 3 Temperature Displays just the temperature reading in large digits If the temperature probe is unplugged the manual temperature setting i...

Page 9: ...Standard Calibration Allowable Conductivity standards are 2 76mS cm for the standard k 1 electrode and 2 8mS cm 58 0mS cm for the optional k 10 electrode The standard should be selected according to your range of interest Place the electrode into a sample of Conductivity standard so that it is immersed at least to the vent hole in the white plastic cover The white plastic cover MUST be in place fo...

Page 10: ...en Conductivity and Salinity modes providing the instrument has been correctly calibrated for both 4 All calibration information is retained in memory when the MC 81 is switched off even when the battery is removed 3 3 Conductivity Calibration Messages 1 If a Zero calibration has been successfully performed the MC 81 will display the following message Zero Cal OK 2 If a Standard calibration has be...

Page 11: ...bration 8 Standard Calibration Allowable Salinity standards are 2 00 ppK for the standard k 1 electrode and 2 0 ppK 36 0 ppK for the optional k 10 electrode The standard should be selected according to your range of interest Place the electrode into a sample of Salinity standard so that it is immersed at least to the vent hole in the white plastic cover The white plastic cover MUST be in place for...

Page 12: ...n Salinity and Conductivity modes providing the instrument has been correctly calibrated for both 4 All calibration information is retained in memory when the MC 81 is switched off even when the battery is removed 4 3 Salinity Calibration Messages 1 If a Zero calibration has been successfully performed the MC 81 will display the following message Zero Cal OK 2 If a Standard calibration has been su...

Page 13: ...anation Place both electrodes into a small sample of pH6 88 or pH7 00 buffer so that the bulb and reference junction are both covered DO NOT place the electrodes directly into the buffer bottle Discard the used buffer after use 8 When the reading has stabilised press and hold the key for 2 seconds to calibrate If a 1 point calibration has been performed the will not be removed until a full 2 point...

Page 14: ...onds to the buffer that you are using 5 3 pH Calibration Messages 1 If a 1 point calibration has been successfully performed the MC 81 will display the following message and then display the asymmetry of the electrode eg 1 Point then Asy 6 88 OK 0 10 pH 2 If a 1 point calibration has failed the MC 81 will display the following message then the failed asymmetry value of the electrode eg 1 Point the...

Page 15: ... tip of the sensor but better temperature response is achieved by immersing the sensor to at least the level of the vent hole in the white plastic cover 5 When the reading has stabilised press and hold the key for 2 seconds 6 The reading from the probe is now displayed on the top line and the value you are going to set is on the bottom line eg 25 0 o C 26 0 7 Press the and keys until the bottom li...

Page 16: ...en Offset Cal Fail 10 5o C 6 4 Manual Temperature Setting 1 Press the key if the meter is not already switched on 2 Press the key until the meter is in Temperature mode 3 Manual temperature setting is only available if the Conductivity sensor is not connected 4 Press and hold the key for 2 seconds 5 The display should now look like this Man Temp 25 0 6 Press the and keys until the bottom line show...

Page 17: ...OLD the key for 3 seconds 3 The display should now look like this Either ON or OFF 9 00V 9 00V 4 In this mode use the or keys to toggle the battery saver function on or off NOTE The display also shows the battery volts This gives the operator an idea of how much battery life is remaining The symbol flashes when the battery volts drops below 7 50 volts At 6 00 volts the meter turns itself off 5 Whe...

Page 18: ... and pH7 00 buffers 5 Press the key to save the primary buffer 6 The display will now show the currently selected high pH buffer Use the or keys to alternate between pH9 23 and pH10 00 buffers the display shows pH10 0 for the latter but this buffer is stored as pH10 00 7 Press the key to save the high pH buffer 8 The buffer recognition setting is kept in memory when the meter is switched off even ...

Page 19: ... hold the key while switching the MC 81 the on with the key 3 The following messages should be displayed Memory then You MUST then TPS MC81 Reset Re Cal Con Sal pH 4 The meter then displays Conductivity and pH Note that the decimal points have been replaced with a to indicate that the unit requires re calibration NOTE When the MC 81 is initialised the automatically recognised buffers are re set to...

Page 20: ...mory Failed Calib Lost Memory Reset You MUST Re Cal User calibration settings have been lost or corrupted Re calibrate the instrument Both a Zero and a Standard calibration will be required for Conductivity and Salinity see sections 3 1 and 4 1 A full 2 point calibration will be required for pH see section 5 1 and a 1 point calibration for temperature see section 6 1 Meter displays the word OFF an...

Page 21: ...dard solution is inaccurate 5 Electrode is faulty Immerse electrode at least to the vent hole in the white plastic cover Clean electrode as per the instructions detailed in section 12 4 Electrode requires replatinisation Return to the factory or see details in section 12 5 Replace standard solution Return electrode to factory for repair or replacement Standard calibration fails and span is greater...

Page 22: ...ory or see details in section 12 5 Readings drift 1 Electrode may have a build up of dirt or oily material on electrode wires Clean electrode as per the instructions detailed in section 12 4 Readings are low or near zero 1 Electrode may have a build up of dirt or oily material on electrode wires 2 Electrode is not immersed deeply enough 3 Electrode is faulty Clean electrode as per the instructions...

Page 23: ...ich the MC 81 has been set to automatically recognise See section 8 Clean glass bulb as per instructions supplied with the electrode Attempt rejuvenation as per instructions supplied with the electrode If not successful replace electrode Dry in a warm place Replace buffers Unstable readings 1 Reference junction blocked 2 Glass bulb not clean 3 Bubble in glass bulb 4 Faulty connection to meter 5 Re...

Page 24: ...uctivity sensor is connected 1 Faulty temperature sensor in conductivity sensor Fit new conductivity sensor NOTE Conductivity readout may still be accurate Displays OVR o C in Conductivity Temp and Salinity Temp modes when conductivity sensor is connected 1 Faulty temperature sensor in conductivity sensor 2 Faulty instrument Fit new conductivity sensor NOTE Conductivity readout may still be accura...

Page 25: ...he registration section returned to TPS Pty Ltd within 7 days No claims will be recognised without the original guarantee card or other proof of purchase This warranty becomes invalid if modifications or repairs are attempted by unauthorised persons or the serial number is missing PROCEDURE FOR SERVICE If you feel that this equipment is in need of repair please re read the manual Sometimes instrum...

Page 26: ...ese amounts are not applicable to full account customers Your equipment will be repaired and returned to you by air express where possible For out of warranty units a repair cost will be calculated from parts and labour costs If payment is not received for the additional charges within 30 days or if you decline to have the equipment repaired the complete unit will be returned to you freight paid n...

Page 27: ...s 2 Excess fertiliser is used in mixes 3 Excessive amounts of soluble fertiliser is used in liquid feed programs 4 Soil containing fertiliser is subject to prolonged over sterilising or sterilising at the wrong temperature 5 Soils are poorly drained 6 Unwashed sand is used in propagation mixes 7 Salt accumulates in porous pots e g clay pots All salts added as fertilisers are potential hazards in t...

Page 28: ...Take samples from areas of poor growth 1 Using a spade clear the growth from the top of the soil being careful not to remove any soil 2 Dig a small hole with straight sides 3 Take a 1 cm thick slice from the side of the hole to a depth of 15 cm or 5 cm for turf If the subsoil occurs before 15 cm take the sample from the top soil only 4 Repeat this process 10 times over the area to be checked 5 Mix...

Page 29: ... screw topped glass or plastic jar with a capacity of about 250ml 2 Add 200ml of distilled or deionised water 3 Shake thoroughly every 5 minutes for 1 hour OR Shake thoroughly after adding water leave stand overnight and shake thoroughly again the next morning 4 Allow the suspension to settle for 15 minutes or longer 5 Measure the Conductivity Salinity or pH by dipping the electrodes just into the...

Page 30: ... stopped draining while in a fairly tall pot 3 Select a straight sided screw top jar of about 400ml capacity 4 Pour into it 100ml of water Mark where this comes to Pour the water out 5 Fill about 120ml of moist loose mix into the jar Firm it gently with the fingers and by light dumping Add more mix if the volume is below 100ml or take some out if it is above 6 Add 150ml of distilled or deionised w...

Page 31: ...itive crops especially at high temperatures in the daytime and with low water application rates Class 3 500 to 1500 ppM High Salinity Water cannot be used on soils with restricted drainage Even with adequate drainage special management techniques for salinity control may be required and the salt tolerance of the crops to be irrigated must be considered Class 4 1500 to 3500 ppM Very High Salinity W...

Page 32: ...red dry Ensure that the electrode is stored in a covered container to avoid dust and dirt build up 12 4 2 Cleaning of Conductivity of Electrodes Platinised platinum Conductivity electrodes can only be cleaned by rinsing in a suitable solvent DO NOT wipe the electrode wires as this will remove the platinum black layer 1 Rinsing in distilled water will remove most build ups of material on the electr...

Page 33: ...se the electrode in platinising solution at least to the vent hole in the white plastic cover Platinising solution is available from TPS part no 122300 Alternatively platinising solution can be prepared by dissolving 1g of Hydrogen Chloroplatinate H2PtCl16 in 30mL of distilled water and including about 0 01g of Lead Acetate CH3COO 2Pb and a drop or two of concentrated HCl 4 Apply a direct current ...

Page 34: ... junction A saturated solution of KCl is used to make contact with the sample It is vital that the KCl solution has an adequate flow rate in order to obtain stable accurate pH measurements 12 6 1 Asymmetry of a pH Electrode An ideal pH electrode produces 0 mV output at 7 00 pH In practise pH electrodes generally produce 0 mV output at slightly above or below 7 00 pH The amount of variance from 7 0...

Page 35: ...actice pH electrodes usually produce slightly less than this The output of a pH electrode is expressed as a percentage of an ideal electrode For example an ideal electrode that produces 59mV pH unit has 100 Slope An electrode that produces 50 15mV pH unit has 85 Slope see Figure 12 2 600 400 200 0 200 400 600 0 7 14 85 Slope at 25 oC 50 15mV pH 100 Slope at 25 oC 59mV pH Response of pH Electrode a...

Page 36: ... 12 3 12 7 Checking the reference junction of a pH electrode If pH readings are inaccurate or unstable the reference junction of the electrode may be blocked The following test can be performed to determine if the reference junction of a pH electrode is making adequate contact with the sample solution 1 Calibrate the MC 81 as per section 5 1 2 Dilute 1 part of pH6 88 buffer with 9 parts of distill...

Page 37: ...uires servicing 6 Now carefully disconnect the wire from the centre pin only make sure the other end of the wire remains connected to the outside frame of the connector 7 After and initial small jump the reading should steadily drift away from 7 00 either up or down at a rate of approximately 1 pH or less every 3 seconds If the drift rate is faster than this then input circuitry of the MC 81 is fa...

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