2262 user manual booklet
Contents
1. The model 2262 is designed to fit in a thermocouple head assembly which is then mounted on to a pipeline pH or ORP electrode This produces a very simple cost effective solution As standard the 2262 offers automatic temperature compensation when connected to a Pt100 sensor other sensor types are available embedded in the electrode Although a separate temperature sensor could be used an electrode with an integral sensor simplifies buffering as the electrode junction and the temperature sensor are always at the same temperature If automatic temperature compensation is not required a resistor with a value near that of the Pt100 may be fitted across the terminals of the 2262 This value does not have to be precise as any error will be calibrated out during buffering CABLE PREPARATION amp ELECTRODE CONNECTION The model 2262 uses screw terminals to connect the electrode temperature sensor amp 4 20mA signal so any connectors on the electrode must be removed Normally the electrode has a thin screened cable and the temperature sensor has two single wires or a twin non screened cable Cut the cables to a length of approximately 75 100mm 3 4 from the top of the electrode If the electrode has a rubber sleeve around the cable this may have to be cut back to the top of the electrode To prepare the screened cable start by remove approximately 20mm 3 4 of the outer insulation This exposes the screen which is woven into a tube arou2. must connect a resistor in place of the temperature sensor For a Pt100 this will usually be 110ohms which represents approximately 25 C TEM PERATURE pH eLecrrope This value should be satisfactory for temperatures in See SCREEN the range 0 50 C There is a table shown later which CENTRE gives Pt100 resistance values for standard temperatures The value is not that critical as it is trimmed out when buffering Once the wires are connected the excess cable can be coiled up under the body of the transmitter before bolting into place using the screws provided MEASURE 100_500mV The 4 20mA cable is usually a twisted pair which is inserted through the gland on the side of the head assembly and stripped back as described for the sensor wires This cable may have an outer screen Screened cables should only be grounded at one 4_20mA 10 30V DC end usually back at the control panel In this case the screen should be cut back so that it can not accidentally short against any of the other wires or terminals A bit of insulating tape or heat shrink can help Tightening the gland should compress a rubber sleeve around the cable so that it is watertight and cannot be pulled out If the wire is too small some insulation tape or heat shrink may be used to increase the diameter as required GROUND LOOPS There is a possibility of ground loop problems if either side of the power supply to the model 2262 is grounded to
3. the liquid being measured This is often a problem with metal tanks in an outdoor environment and especially with distributed systems such as PLC s and PC s A ground loop is caused by leakage currents through the solution from the pH electrode and usually manifests itself by causing the instrument to drive hard upscale or downscale For applications where ground loops are possible it is recommended that a 4 20mA signal isolator such as the model 1120 be used to break the loop If you suspect a ground loop problem try the following After checking the instrument calibration place a sample of the process liquid in an insulated container such as a glass beaker or a plastic bucket and place the pH electrode in this container Make a note of the reading Next place the pH electrode in the process liquid tank and take another reading If the two readings are dramatically different the chances are you have a ground loop CALIBRATING THE ELECTRODE BUFFERING pH CALIBRATION TABLE As electrodes usually have offset and slope errors compared to the theoretical values the transmitter needs to be calibrated to the electrode These errors change as the electrode ages and PA mA mA regular recalibration should be carried out as often as needed pot 000 oof ff pH Electrodes eee a For this operation you will require beakers containing distilled water 7pH buffer solution and 4pH 3 21 43 7 43 10 00 5 60 or 10pH buffer solution The choice of 4pH or 1
4. 0pH buffer solution depends on whether your ee eer ee eee n process tends towards high or low pH values Always try to use a buffer as close as possible to your e 2286 10 86 40 00 10 40 3333 9 33 process value for best results 7 50 00 1200 50 00 12 00 50 00 12 00 You will also need a way to measure the 4 20mA output current You may be able to do this by 8 5714 1314 60 00 13 60 66 67 14 67 reading the display on your control instrument or by inserting a mA meter or calibrator in series with Shes 1429 00 15 20 Sass 17 85 one lead of the transmitter eee ea ee eo eee 140 A neat trick is to fit a 1N4004 or similar silicon diode in series with the 4 20mA signal A multimeter 12 8571 1771 100 00 20 00 set to a current range may be connected across this diode at any time to take current 13 9286 1886 measurements without disconnecting the 4 20mA loop Because the voltage drop across the 14 10000 200 multimeter will be less than the 0 7V drop across the diode when the meter is connected no CU Hee a cIOge RESISTANCE VALUES FOR TEMPERATURE SENSORS The following procedure uses values for the model 2262 ranged 0 14pH A table follows with values Temp Pii00 Nees Neuen Pr 1000 Neamt Neaga for other calibrations Standard Practical Standard Practical 1 Rinse the electrode in distilled water and place in 7pH buffer When the output has o 10 1o tabilised trim the STD ad
5. SPECIFICATIONS POWER 9 36V DC SUPPLY OUTPUT 4 20mA SIGNAL INPUT Any standard pH or ORP combination electrode INPUT IMPEDANCE gt 30GS RANGE 0 14pH options 2 12pH 4 10pH 1000 1000mV 2000 2000mV ADJUSTMENT Standardize 1pH Slope 50 105 of nominal electrode output ACCURACY lt 0 2 F S typical TEMPERATURE COMPENSATOR Pt100 Standard Pt1000 Ni3000 Balco optional OPERATING 5 to 65 C TEMPERATURE AMBIENT 0 to 90 RH HUMIDITY Non Condensing MODEL 2262 pH ORP TRANSMITTER USER MANUAL Revision Date 20041201 H a Model 226207 1 A oe Pt1000 7993 U Sa number poe pH amp ORP oxygen reduction potential or redox electrodes are high impedance devices which produce a mV signal proportional to the pH or ORP of a solution It is not always easy to use this signal directly for process control applications especially where the electrode is mounted a long distance from the instrument The model 2262 solves this problem by converting the signal from the electrode into a standard 4 20mA process signal The 4 20mA signal is an industry standard which can be used with simple alarm circuitry or sophisticated PLC and computer monitoring systems 4 20mA signals have three advantages over voltage signals for industrial applications 1 Better noise immunity 2 Longer cable runs because cable resistance does not affect calibration 3 Only two wires are required to provide both power and signal
6. justment to get a reading of 12 00mA 50 ae i hei l 2 Rinse the electrode in distilled water and place in 4pH or 10pH buffer When the output has stabilised trim the Slope adjustment to get a reading of 8 57mA 28 6 or 15 43mA 20 tore 17 t078 1070 71 4 oe i ii 110 ia 3 No further adjustments should be required but for peace of mind it is worth repeating the procedure from the beginning as a check Note 1 The response time of this transmitter is quite slow Make sure you wait a few seconds 120 until the reading is stable before making adjustments Note 2 When adjusting the trimmers you may notice a small change in reading after you take your hand away from the transmitter The signal pin is not screened and it can pick up 50 60Hz hum if you hold your hand close to it This is more noticeable with very high impedance electrodes such as double junction types Once the transmitter is calibrated o 1309 130 130 and the lid fitted this is not a problem Some people seem to generate more noise than others a long screwdriver can help p90 137 i
7. nd an inner insulator With the help of a pointed object separate the wires in the screen back to the cut end of the outer insulator and twist the wires together to form a single conductor we The inner insulation is usually white or translucent but it may be covered by a thin black coating This coating is electrically conducting and forms part of the screen Remove this coating as far back as possible taking care not to damage the inner insulation If left this coating could make contact with the inner conductor shorting out the signal from the electrode Now remove approximately 10mm 3 8 of the inner insulator exposing the inner conductor This is usually made up of several thin wires which should O be twisted together for strength The inner conductor amp screen may be tinned using a soldering iron The insulation of the temperature compensator wires should also be stripped back approximately 10mm and soldered if required Now screw the electrode tightly into the bottom of the head assembly Remove the lid from the head assembly and insert the model 2262 transmitter passing the cables through the hole in the centre At this stage you may wish to solder or crimp spade connectors on to the wires You now have four wires and three terminals The centre terminal is a common for both the electrode and the temperature sensor To the terminal connect the screen from the electrode and one of the temperatu
8. ow you will have to calculate the reading you require For ORP transmitters the slope adjustment should be sealed This is a factory adjustment and should only be used when calibrating the transmitter against an accurate millivolt source Note There is a conflict between European and American standards as to which polarity is used for oxidizing and reducing If the output of the transmitter gives a reverse polarity reading with your instrumentation then you should reverse the electrode wires and recalibrate using the values in the reversed polarity columns mV at Range 1000 1000mV Range 2000 2000mV 25 C Polarity Normal Polarity Reversed Polarity Normal Polarity Reversed gt ml o my ml e saa o 7 tsi s2 eas as ELECTRODE CONTAMINATION Various chemicals can affect the readings taken by a pH ORP electrode by contaminating one or other of the junctions Sometimes the contamination is temporary and can be reversed by washing the electrode other times it can be permanent Special electrodes such as double junction types are available for these applications Below is a list of some of the more problematic chemicals however it is advisable to consult your electrode supplier before ordering Sodium ions Na Proteins Heavy Metals Organic Compounds Bromides lodides Sulphides Cyanides Any compounds which interact with silver Vegetable Oils If you are using an electrode without a temperature sensor then you
9. re sensor wires the sensor is not polarised so either will do The other electrode wire goes to the terminal marked pH and the other temperature sensor wire goes to the terminal marked Temp TAKING CARE OF YOUR ELECTRODE Electrode Storage For best results always keep the pH bulb wet preferably in pH 4 00 buffer with 1 100 parts of saturated KCI added Other pH buffers or tap water are acceptable storage media but avoid storage in distilled water The protective boot supplied with the electrode will provide an ideal storage chamber for long periods Some evaporation can occur so check the liquid every couple of months and top up if necessary Wrapping plumber s PTFE tape around the join between bulb and electrode will reduce evaporation Store in a cool place but do not allow to freeze Electrode Cleaning Electrodes which are mechanically intact with no broken parts can often be restored to normal performance by one of the following procedures 1 Salt deposits Dissolve the deposit by immersing the electrode in 0 1M HCI for five minutes followed by immersion in 0 1M NaOH for five minutes and thoroughly rinsing with distilled water 2 Oil Grease Films Wash electrode pH bulb in a little detergent and water Rinse electrode tip with distilled water 3 Clogged Reference Junction Heat a diluted KCI solution to 60 80 degrees C Place the sensing portion of the pH electrode into the heated KCI Solution for approximately 10 min
10. utes Allow the electrode to cool while immersed in some unheated KCI Solution 4 Protein deposits Dissolve the deposit by immersing the electrode in a 1 pepsin solution with a background of 0 1M HCI for five minutes followed by thorough rinsing with distilled water If these steps fail to restore normal electrode response replace the electrode Shelf Life The recommended shelf life of a pH or ORP electrode is six months Most will still work successfully after two years if properly stored Buffer solutions have varied shelf lives and it is best to confirm this with the manufacturer Most buffers will last at least 12 months if kept sealed Some 10pH buffers grow a mould when left for an extended period Often a 9pH buffer is a better option for use in field kits ORP Electrodes ORP electrodes are calibrated in a similar way to pH electrodes however only a single point calibration in buffer is used The most popular ORP buffer solutions are probably 86mV 220mV 263mV and 476mV Try to pick one which is close to the value you expect to be measuring Some of the ORP buffers require activators and need continuous agitation to get a stable reading 1 Rinse the electrode in distilled water and place in chosen buffer stirring if required When the output has stabilised trim the Standardise adjustment to get the correct reading from the values shown in the following table 10mV If you are using a buffer with a value not shown bel
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