Emerson designs, manufactures, and tests its products to meet many national and international standards. Because these
instruments are sophisticated technical products, you must properly install, use, and maintain them to ensure they continue to
operate within their normal specifications. The following instructions must be adhered to and integrated into your safety program
when installing, using, and maintaining Emerson products. Failure to follow the proper instructions may cause any one of the
following situations to occur: loss of life, personal injury, property damage, damage to this instrument, and warranty invalidation.
• Read all instructions prior to installing, operating, and servicing the product.
• If this Reference Manual is not the correct one, call 1-800-999-9307 to request the correct Reference Manual. Save this
Reference Manual for future reference.
• If you do not understand any of the instructions, contact your Emerson representative for clarification.
• Follow all warnings, cautions, and instructions marked on and supplied with the product.
• Inform and educate your personnel in the proper installation, operation, and maintenance of the product.
• Install equipment as specified in the installation instructions of the appropriate Reference Manual and per applicable local and
national codes. Connect all products to the proper electrical and pressure sources.
• To ensure proper performance, use qualified personnel to install, operate, update, program, and maintain the product.
• When replacement parts are required, ensure that qualified people use replacement parts specified by Emerson.
Unauthorized parts and procedures can affect the product's performance, place the safe operation of your process at risk, and
VOID YOUR WARRANTY. Look-alike substitutions may result in fire, electrical hazards, or improper operation.
• Ensure that all equipment doors are closed and protective covers are in place, except when maintenance is being performed
by qualified people, to prevent electrical shock and personal injury.
WARNING
Hazardous area installation
Installations near flammable liquids or in hazardous area locations must be carefully evaluated by qualified on site safety
personnel.
To secure and maintain intrinsically safe installation, use an appropriate transmitter/safety barrier/sensor combination. The
installation system must be in accordance with the governing approval agency (FM, CSA, or BASEEFA/CENELEC) hazardous are
classification requirements. Consult your transmitter Reference Manual for details.
Proper installation, operation, and servicing of this sensor in a hazardous area installation are entirely the operator's
responsibility.
CAUTION
Sensor/process application compatibility
The wetted sensor materials may not be compatible with process composition and operating conditions.
Application compatibility is entirely the operator's responsibility.
CAUTION
Software modifications
If a 275, 375, or 475 Universal HART® Communicator is used with these transmitters, the software within the 275, 375, or 475
may require modification.
If a software modification is required, please contact your local Rosemount Service group or National Response Center at
1-800-654-7768.
2
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Contents
Chapter 1Description and Specifications....................................................................................... 5
1.1 Features and applications................................................................................................................. 5
Rosemount 389VP triple-junction sensors are offered with SMART capabilities. SMART
options are enabled when used with Rosemount 1056, 1057, 1066, and 56 transmitters.
The pH-loop capabilities include auto-recognition of the SMART sensor, automatic upload
of calibration data and associated time stamp, and historical recording of pH diagnostics
(slope, offset, reference impedance, and glass impedance). This trending data allows
technicians to predict frequency of maintenance and estimate sensor life for a particular
process condition. Additional SMART features include factory calibration, resetting SMART
sensor calibration data with user menus without power cycling, and manufacturing
information.
The reference junction aids in the sensor's resistance to poisoning ions and helps
prolong sensor life. Rosemount 389/389VP sensors have a triple junction reference, which
protects the reference element from poisoning ions - such as ammonia, chlorine,
cyanides, and sulfides - in the process. Both models are made with anouter ceramic
junction constructed in an annualr design around the pH/ORP sensitive membrane.
The AccuGLASS™ pH glass formulations exceed industry standards. The AccuGlass pH
glass is a result of many years of glass research resulting in a formulation which has been
found to increase the life of the sensor. Unlike other pH glasses presently on the market,
this glass resists cracking, especially at higher temperatures, and reduces sodium ion
errors commonly found in high pH applications. Overall, the AccuGlass formulation
enhances the sensor performance to measure pH more accurately and have a longer
sensor life than ever before.
A choice of pH glass electrodes is available to best meet various application needs. Two
types are available: general purpose and high pH glass. The AccuGlass hemi bulb is the
standard glass offered on both types and can be used for most applications.
The Rosemount 389VP is configured with a Variopol (VP8) sensor-to-cable connector
which eliminates re-wiring and cable twisting when replacing sensors. The Variopol VP8
multiple pin connector option uses a mating VP cable. Once the cable is installed and
wired to the transmitter, sensors are easily replaced without replacing the cable and
without rewiring the transmitter. Also, the cable can be disconnected from the sensor
before removal from the process which eliminates cable twisting. VP8 cable assemblies
work with both VP8 and VP6 sensor connectors.
The Rosemount 389/389VP has a molded Tefzel body with Viton O-rings, making each
sensor very robust and chemically resistant. Complete encapsulation eliminates leakage or
high humidity problems traditionally found in other pH/ORP designs. The seimplified
construction, designed with user convenience in mind, does not require electrolyte (KCl)
replenishment or any high maintenance troubleshooting procedures.
Rosemount 389/389VP sensors are combintation sensors (pH, reference, and
temperature within sensor body) and measure pH or ORP (oxidation/reduction potential)
of aqueous solutions in pipelines, open tanks, or ponds. rosemount 389/389VP sensors are
suitable for virtually all applications and are compatible with Rosemount and other
manufacturers' instruments.
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Description and SpecificationsReference Manual
February 201900809-0100-3389
Installation is easily achieved through the wide variety of mounting configurations.
These sensors feature a 1 inch (MNPT) front and rear facing connections for insertion,
submersion, or flow-through pH and ORP applications.
Automatic temperature compensation : 32 to 185 °F (0 to 85 °C)
Maximum pressure
100 psig (790 kPa[abs]) at 150 °F (65 °C) - see Figure 1-1
Materials of construction
Sensor bodyTefzel
pH electrodeGlass
ORP electrodePlatinum
JunctionCeramic
O-ringViton
Process connections
Front facing1 in. MNPT
Rear facing1 in. MNPT
Cable
389Integral preamplifier - 25 ft (7.8 m); no preamplifier - 15 ft
(4.6 m)
389VPUse 24281-XX, 2.5 ft (0.8 m) to 100 ft (31 m) (see
Accessories)
Weight/shipping weight
1 lb / 2 lb (0.45 kg / 0.9 kg)
6Rosemount 389/389VP
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Figure 1-1: Pressure/temperature operating range for Rosemount 389/389VP
1.3Certifications
IECEx
Sensors without preamp (pH and ORP): Ex ia IIC T4 Ga (-20 ºC ≤ Ta ≤ +60 ºC)
Sensors with SMART preamp (pH only): Ex ia IIC T4 Ga (-20 ºC ≤ Ta ≤ +60 ºC)
Sensors with standard preamp (ORP only): Ex ia IIC T4 Ga (-20 ºC ≤ Ta ≤ +80 ºC) or Ex IIC T5
Ga (-20 ºC ≤ Ta ≤ +40 ºC)
Per standards IEC60079-0: 2011, IEC 60079-11: 2011
ATEX
Sensors without preamp (pH and ORP): II 1 G Ex ia IIC T4 Ga (-20 ºC ≤ Ta ≤ +60 ºC)
Sensors with SMART preamp (pH only): II 1 G Ex ia IIC T4 Ga (-20 ºC ≤ Ta ≤ +60 ºC)
Sensors with standard preamp (ORP only) - II 1 G Ex ia IIC T4 Ga (-20 ºC ≤ Ta ≤ +80 ºC) or II 1
G Ex ia IIC T5 Ga (-20 ºC ≤ Ta ≤ +40 ºC)
Per standards EN 60079-0:2012 + A11:2013, EN 60079-11:2012
FM
See online FM Certificate of Compliance for applicable sensor options:
Intrinsically safe for use in Class I, II, and III, Division 1, Groups A, B, C, D, E, F, and G;
Temperature Class T6 Ta = -20 °C to + 60 °C
Intrinsically safe for use in Class I, Zone 0, AEx ia IIC T6 Ta = -20 °C to + 60 °C
Nonincendive for use in Class I, Division 2, Groups A, B, C, and D; Temperature Class T6 Ta
= -20 °C to + 60 °C
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Suitable for use in Class II and III, Division 2, Groups E, F, and G; Temperature Class Ta = -20
°C to + 60 °C Hazardous (Classified) Locations
IS/I, II, III/1/ABCDEFG/T6 Ta = 60 °C - 140332; Entity: I/0/AEx ia IIC/T6 Ta = 60 °C - 1400332;
Entity; NI/I/2/ABCD/T6 Ta = 60 °C; S/I, III/2/EFG/T6 Ta = 60 °C; Entity Parameters
Per standards 3600: 1998; 3610: 2010, 3611:2004, 3810:2005
CSA
See online CSA Certificate of Compliance for applicable sensor options:
Intrinsically Safe: Class I, Division 1, Groups ABCD; Class II, Division 1, Groups EFG; Class III,
Class I, Division II, Groups ABCD; Ambient temperature rating -20 °C to + 60 °C; Ex ia IIC; T6
Intrinsically Safe and Non-Incendive: Class I, Division 1, Groups ABCD; Class II, Division 1,
Groups EFG; Class III; Class 1, Division 2, Groups ABCD; Ex ia IIC; T6; Ambient temperature
rating -20 °C to + 60 °C: (Simple Apparatus)
Class I, Division 1, Groups ABCD; Class II, Division 1, Groups EFG; Class III; Class I, Division 2,
Groups ABCD; Ex ia IIC; T6; Ambient temperature rating -20 °C to + 60 °C: (Simple
Apparatus)
Per standards C22.2 No. 144 -M1987, C22.2 No 157 - M1992, CAN/CSA E60079:0:07,
CAN/CSA E60079:11:02, UL 50, UL 508, UL 913, UL 60079-0:2005, UL 60079-11: 2002
1.4Ordering information
The Rosemount 389 and 389VP General Purpose pH/ORP Sensors are housed in a molded
Tefzel body with 1 in. MNPT forward and rear facing threads suitable for insertion,
submersion, or flow through installation. The sensors can be configured with a general
purpose pH, high pH, or platinum ORP electrode. Rosemount 389VP sensors are offered
with SMART preamplifiers for pH measurements and standard integral preamplifiers for
ORP measurements. These sensors may be configured without a preamplifier, but must be
used with a remote preamplifier (j-box or transmitter). Automatic temperature
compensation is standard. Sensors are available with either an integral cable connection
(389) or Variopol (VP6) connector (389VP). Variopol cables sold separately (see Table 5-2).
Table 1-3: Rosemount 389 pH/ORP Sensor ordering information
ModelSensor type
389pH/ORP Sensor
Preamplifier/cable
01Integral pramplifier, 25 ft cable
02No preamplifier, 15 ft cable
(1)
Combination electrode
10pH -GPLR glass
11pH-high pH glass
12ORP
8Rosemount 389/389VP
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Table 1-3: Rosemount 389 pH/ORP Sensor ordering information (continued)
Transmitter/TC compatibility
501181, 1050, 1060 (code -01 or -02)
541054A/B, 81, 2081, (code -01 or -02); for 54, 56, 1055, 1056, 1057, 1066, 5081, 6081, and XMT (code
(1) Only available with -10, -11, and -55 options.
(1)
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10Rosemount 389/389VP
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2Install
2.1Unpacking and inspection
Procedure
1. Inspect the outside of the carton for any damage.
2. If damage is detected, contact the carrier immediately.
3. Inspect the hardware.
4. Make sure all the items in the packing list are present and in good condition.
5. Notify the factory if any part is missing.
2.2Mounting
The sensor has been designed to be located in industrial process environments.
Temperature and pressure limitations must not be exceeded at any time. A label regarding
this matter is attached to the sensor with the cable and should not be removed.
A. VP (Variopol Connection)
B. 1-in. wrench opening
C. 1-in. MNPT x 2
D. T.C.
E. pH/ORP electrode
WARNING
IRRITANT
Internal electrolyte fill may cause skin or eye irritation.
Mounting guidelines
1. Shake down the sensor to remove any air bubbles that may be present inside the tip
of the pH glass.
2. Do not install the sensor horizontally. The sensor must be 10° off the horizontal to
ensure accuracy.
3. Do not install the sensor upside down.
4. With the standard recessed electrode, air bubbles may become trapped in the
sensor end. This problem is most commonly encountered in areas of low flow or
during calibration. Shake the probe while it is immersed in solution to remove
bubbles.
12Rosemount 389/389VP
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In most cases, the sensor can simply be installed as shipped, and you can obtain readings
with an accuracy of ±0.2 pH. To obtain greater accuracy or to verify proper operation, the
sensor must be calibrated as a loop with its compatible analyzer or transmitter.
2.2.1Submersion mounting
Rosemount 389 and 389VP Sensors have a 1-in. MNPT process connection at the back of
the sensor.
Procedure
1. To prevent rain water or condensation from running into the sensor, use a
weatherproof junction box (see Figure 2-3).
2. Using a standard 1-in. union, mount the sensor to a 1-in. SCH 80 CPVC or PVDF
standpipe.
3. Tapered pipe threads in plastic tend to loosen after installation. We therefore
recommend that you use PTFE tape on the threads and check the tightness of the
connection frequently to ensure that no loosening has occurred.
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Figure 2-3: Submersion Installations
Reference Manual
4. Run the sensor cable through a protective conduit for isolation from electrical
interference or physical abuse from the process.
5. Install the sensor within 80° of vertical, with the electrode facing down.
Do not run the sensor's cable with power or control wiring.
2.2.2
14Rosemount 389/389VP
Flow through and insertion mounting
Rosemount 389 and 389VP sensors also have a 1-in. MNPT process at the front of the
sensor for mounting into a 1¼-in. tee or the process. See Figure 2-4 for installation
configurations.
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00809-0100-3389February 2019
Figure 2-4: Flow Through and Insertion Installations
A. Angle flow
B. Straight flow
C. Pipe "Y"
D. 1½-in. x 1-in. reducing bushing
E. 1½-in. pipe tee
F. 1½-in. pipe "Y"
G. flow
Install
Note
Valves and fittings by others. Mount the sensor at least 10° from horizontal.
Note
Do not use large pipe wrenches to tighten the sensor into a flange or other type of
mounting.
2.3Electrical installation
Figure 2-5 through Figure 2-19 provide the guidelines for wiring Rosemount 389/389VP
sensors to various Rosemount transmitters.
1. If the cable needs to be extended, use a high quality four-conductor shielded
instrument cable available from Rosemount.
Note
If the cable is too long, loop up the excess cable. If the cable has to be shortened,
splice and terminate each conductor and make sure that the overall (outermost)
drain wire is not shorted out with either of the two inner drain wires (shields).
2. Signal cable should be run in a dedicated conduit (preferably an earth grounded
metallic conduit) and should be kept away from AC power lines. A spade lug kit is
provided in a plastic bag wrapped around the cable.
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Figure 2-5: Rosemount 389 with Insertion Mounting Adapter P/N 23242-02
A. Cable
B. ¾-in. FNPT
C. Peek adapter; 1-in. PNPT x ¾-in. FNPT (reversible)
D. 2-135 Viton "O" ring
Note
"O" ring must be inplace prior to use (PN 9550175)
E. Nut, hex union 2-in.; 3-in. wrench opening (304 SST)
F. 2.531.8 ACME thread (TYP)
G. Neck, union fitting (316 SST); 2 5/8-in. wrench opening
H. 1½-in. MNPT
Figure 2-6: VP 8 Cable, Rosemount 389VP Sensor End
16Rosemount 389/389VP
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Figure 2-7: VP8 Cable, Instrument End
A. Earth ground
B. ID
Note
For additional wiring information on this product, including sensor combinations not
shown here, refer to the Liquid Transmitter Wiring Diagrams.
C. Solution ground
D. Note
For additional wiring information on this product, including sensor combinations not
shown here, refer to the Liquid Transmitter Wiring Diagrams.
E. Ref in
F. pH/mV IN
G. pH/mV SHIELD
H. RTD return
I. RTF sense
J. RTD IN
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Figure 2-8: Rosemount 389-01-xx-55 Wiring to Rosemount 1056, 1057, and 56
Transmitters
18Rosemount 389/389VP
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Figure 2-9: Rosemount 389-01-xx-55 Wiring to Rosemount 1066 Transmitter
Figure 2-10: Rosemount 389-01-xx-55 Wiring to Rosemount 5091 Transmitter
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Figure 2-11: Rosemount 389VP Wiring to Rosemount 1056, 1057, and 56
Transmitters
20Rosemount 389/389VP
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Figure 2-12: Rosemount 389VP Wiring to Rosemount 1066 Transmitter
Figure 2-13: Rosemount 389VP Wiring to Rosemount 5081 Transmitter
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Figure 2-14: Rosemount 389VP-xx-55-70 Wiring to Rosemount 1056, 1057, and 56
Transmitters
Figure 2-15: Rosemount 389VP-xx-55-70 Wiring to Rosemount 1066 Transmitter
22Rosemount 389/389VP
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Figure 2-16: Rosemount 389VP-xx-55-70 Wiring to Rosemount 5081 Transmitter
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Figure 2-17: Rosemount 389-02-xx-54-62 Wiring to Rosemount 1056, 56, and 1057
Transmitters
24Rosemount 389/389VP
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Figure 2-18: Rosemount 389-02-xx-54-62 Wiring to Rosemount 1066 Transmitter
Figure 2-19: Rosemount 389-02-xx-54-62 Wiring to Rosemount 5081 Transmitter
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26Rosemount 389/389VP
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Calibration
3Calibration
3.1Sensor preparation
Procedure
1. Shake down the sensor to remove any air bubbles that may be present at the tip of
the pH glass bulb.
2. In most cases, the pH sensor can simply be installed as shipped, and readings may
be obtained with an accuracy of ±0.2 pH. To obtain greater accuracy or to verify
proper operation, calibrate the sensor as a loop with its compatible transmitter.
3.2pH calibration
1. After a temporary connection is established between the sensor and the
instrument, a buffer calibration may be performed.
3.2.1
2. Consult the appropriate pH/ORP transmitter instruction manual for specific
calibration and standardization procedures, or see below for the recommended
two-point buffer calibration procedure.
Recommended two point buffer calibration procedure
Prerequisites
Select two stable buffer solutions, preferably pH 4.0 and 7.0. (pH buffers other than pH 4.0
and pH 7.0 can be used as long as the pH values are at least two pH units apart).
Note
A pH 7 buffer solution reads an mV value of approximately zero, and pH buffers read
approximately ±59.1 mV for each pH unit above or below pH 7. Check the pH buffer
manufacturer specifications for millivolt values at various temperatures, as it may affect
the actual value of the buffer solution mV/pH value.
Procedure
1. Immerse the sensor in the first buffer solution. Allow the sensor to adjust to the
buffer temperature (to avoid errors due to temperature differences between the
buffer solution and sensor temperature) and wait for readings to stabilize.
The value of the buffer can now be acknowledged by the transmitter.
2. Once the first buffer has been acknowledged by the transmitter, rinse the buffer
solution off the sensor with distilled or deionized water.
3. Repeat steps 1 and 2 using the second buffer solution.
Once the transmitter has acknowledged both buffer solutions, a sensor slope
(mV/pH) is established (the slope value can be found within the transmitter). The
slope value should read about 59.1 mV/pH for a new sensor and will decrease over
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February 201900809-0100-3389
time to approximately 47 -49 mV/pH. Once the slope reads below the 47-49 mV/pH
range, install a new sensor to maintain accurate readings.
Reference Manual
3.2.2Recommended pH sensor standardization
For maximum accuracy, the sensor can be standardized in-line or with a process grab
sample after a buffer calibration has been performed and the sensor has been conditioned
to the process. Standardization accounts for the sensor junction potential and other
interferences. Standardization does not change the sensor's slope, but simply adjusts
transmitter's reading to match that of a known process pH.
Procedure
1. While obtaining a process solution sample (we recommend that you take the
sample close to the sensor), record the pH value that is shown on the transmitter
display.
2. Measure and record the pH of the process solution sample with another
temperature compensated, calibrated pH instrument. For best results, perform
standardization at the process temperature.
3. Adjust the transmitter to the standardized value.
3.3Rosemount™ 389/389VP ORP calibration
Most industrial applications have a number of ORP reactions occuring in sequence or
simultaneously. There can be several components that are oxidized or reduced by the
reagents that are used. Theoretically, the ORP potential is absolute, because it is the result
of the oxidation/reduction equilibrium. However, the actual measured potential is
dependent on many factors, including the condition of the surface of the ORP platinum
electrode. Therefore the sensor should be allowed 1-2 hours to become conditioned to the
stream when first set up or after being cleaned.
WARNING
CORROSIVE SUBSTANCE
The solution used during the following check is an acid and should be handled with care.
Follow the directions of the acid manufacturer. Wear the proper protective equipment. Do
not let the solution come in contact with skin or clothing. If contact with skin is made,
immediately rinse with clean water.
Procedure
1. Make a temporary electrical connection between the sensor and the instrument.
2. Obtain a standard solution of saturated quinhydrone (PN R508-16OZ). To make this
solution, add a few crystals of quinhydrone to either pH 4 or pH 7 buffer.
Quinhydrone is only slightly soluble, but only a few crystals are required.
3. Immerse the sensor in the standard solution. Allow one to two minutes for the ORP
sensor to stabilize.
4. Adjust the standardized control of the transmitter to the solution value shown in
Table 3-1.
28Rosemount 389/389VP
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The resulting potentials, measured with a clean platinum electrode and saturated
KCl/AgCL reference electrode, should be within ±20 millivolts of the value shown in
Table 3-1. Note solution temperature to ensure accurate interpretation of results.
The ORP value of saturated quinhydrone solution is not stable over long periods of
time. Therefore, make these standards fresh each time they are used.
Table 3-1: ORP of Saturated Quinhydrone Solution (Millivolts)
pH 4 solutionpH 7 solution
Temp ºC202530202530
mV
potential
268264260948780
5. Remove the sensor from the buffer, rinse, and install in the process.
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30Rosemount 389/389VP
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Maintenance
4Maintenance
Rosemount™ 389/389VP sensors require minimum maintenance. Keep the sensors clean
and free of debris and sediment at all times. The frequency of cleaning by wiping or
brushing with a soft cloth or brush is determined by the nature of the solution being
measured. Remove sensors from the process periodically and check them in buffer
solutions.
WARNING
PRESSURE AND TEMPERATURE
Before removing the sensor, be absolutely certain that the process pressure is reduced to
0 psig and the process temperature is lowered to a safe level!
If the sensor will not calibrate, refer to your transmitter reference manual for proper test
procedures. If you determine that the sensor has failed, discard and replace it.
4.1Clean electrode
If the electrode is coated or dirty, clean as follows:
Procedure
1. Remove the sensor from process.
2. Remove the sensor from process as instructed in Retractable version
3. Wipe the glass bulb with a soft, clean, lint free cloth or tissue. If this does not
remove the dirt or coating, go to Step 4 (detergents clean oil and grease; acids
remove scale.)
4. Wash the glass bulb in a strong detergent solution and rinse it in clean water. If this
does not clean the glass bulb, go to Step 5.
WARNING
CORROSIVE SUBSTANCE
The solution used during the following step is an acid; handle with care. Follow the
directions of the acid manufacturer. Wear the proper protective equipment. Do not
let the solution come in contact with skin or clothing. If contact with skin is made,
immediately rinse with clean water.
5. Wash the bulb in a dilute 5% hydrochloric acid solution and rinse with clean water.
Soaking the sensor overnight in the acid solution can improve cleaning action.
Replace the sensor if it cannot be cleaned.
6. Following the Warning above, wash the glass bult in dilute 5% hydrochloric acid
solution and then rinse it thoroughly with clean tap water. Replace the sensor if it
cannot be clean. If the glass bulb appears clean, proceed to Step 7.
7. Buffer calibrate the sensor.
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Refer to Startup and calibration. If the sensor appears to respond sluggishly to pH
change, soaking it overnight in a weak acid solution (5% hydrochloric acid) may
improve its response. Be sure to follow the Warning above and to rinse the sensor's
tip thoroughly with tap water. If the sensor will not calibrate, it must be replaced.
4.2Automatic temperature compensator
The temperature compensator element is a temperature sensitive resistor and can be
checked with an ohmeter. Resistance increases with temperature.
The 3K element reads 3000 ohms ±1% at 77 °F (25 °C), and a Pt100 reads 110 ohms.
Resistance varies with temperature for a 3K and Pt-100 element and can be determined
according to Table 4-2 or the following formula:
RT = RO [1 + R1(T-20)]
Where RT = Resistance and T = Temperature in °C
Refer to Table 4-1 for RO and R1 values.
Table 4-1: RO and R1 Values for Temperature Compensation Elements
Temperature compensation
element
3K29340.0045
PT-100107.70.00385
R
O
R
1
Table 4-2: Temperature vs. Resistance of Auto T.C. Elements
Temperature °CResistance (Ohms) ±1%
3KPT-100
026270100.0
102802103.8
202934107.7
253000109.6
303066111.5
403198115.4
503330119.2
603462123.1
703594126.9
803726130.8
903858134.6
1003990138.5
32Rosemount 389/389VP
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4.3ORP
4.3.1Check platinum electrode
Check the platinum electrode as follows. There are two types of standard solutions which
may be used to check the ORP electrode/transmitter system.
Type 1: One type of commonly used ORP standard solution is the saturated quinhydrone
solution (PN R508-16OZ). Refer to Rosemount™ 389/389VP ORP calibration.
WARNING
The solution used during the following check is an acid.
Handle the solution with care.
Follow the manufacturer's directions.
Wear the proper protective equipment.
If contact with skin or clothing is made, immediately rinse with plenty of clean water.
4.3.2
Type 2: A second ORP standard solution can be prepared from the following recipe:
Procedure
1. Dissolve 39.2 grams of reagent grade ferrous ammonium sulfate, Fe(NH4)2(SO4)2 ●
6H2O and 48.2 grams of reagent grade ferric ammonium sulfate, FeNH4(SO4)2 ● 12
H2O in approximately 700 ml of water.
Distilled water is preferred, but tap water is acceptable.
2. Slowly and carefully add 56.2 ml of concentrated sulfuric acid.
3. Add sufficient water to bring the total solution volume up to 1000 ml.
This standard ORP solution, although not as simple to prepare as the quinhydrone recipe,
is much more stable and will maintain its millivolt value for approximately one year when
stored in glass containers. This solution (ferric/ferrous ammonium sulfate) produces a
nominal ORO of 476 +20 mV at 77 °F (25 ºC) when used with a saturated KCL/AgCl
reference electrode and platinum measuring electrode. Some tolerance in mV values is to
be expected due to the rather large liquid reference junction potentials that can arise
when measuring this strongly acidic and concentrated solution. However, if measuring
electrodes are kept clean and in good operating condition, consistently repeatable
calibrations can be carried out using this standard solution.
Cleaning platinum electrode
To restore the electrode to normal operation, clean the platinum electrode with baking
soda. Polish it by rubbing it with a damp paper towel and baking soda until it appears
bright and shiny.
Reference Manual 33
Page 34
MaintenanceReference Manual
February 201900809-0100-3389
34Rosemount 389/389VP
Page 35
Reference Manual Troubleshooting
00809-0100-3389February 2019
5Troubleshooting
Table 5-1: Troubleshooting
TroubleProbable CauseRemedy
Meter reads off scale (Display reads
overrange).
Display reads between 3 and 6 pH
regardless of actual pH of solution or
sample.
Meter or display indication swings or
jumps widely in AUTO T.C. Mode.
Span between buffers extremely short
in AUTO T.C. Mode.
Sluggish or slow meter indication for
real changes in pH level.
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