Instruction manual

MODEL XMT-A-FF/FI SECTION 15.0
TROUBLESHOOTING
15.2.5 Need Zero Cal
Need Zero Cal means the measured concentration is a large negative number. The transmitter subtracts the zero current
from the measured current before converting the result to a concentration reading. If the zero current is much greater than
the measured current, the concentration reading will be negative.
1. Check the zero current and the present sensor current. To view the zero current, go to the main display and press

until Zero Current appears. The value shown is the zero current the last time the sensor was zeroed. To view the pres-
ent sensor current, go to the main display and press

until Input Current appears. Note the units: nA is nanoamps,
µA is microamps.
2. Refer to the appropriate section for calibrating the sensor. Place the sensor in the zero solution. Verify that the sensor
reading is within or at least very close to the zero current limits. It may take as long as overnight for the sensor to reach
a stable zero current.
15.2.6 pH mV Too High
This message means the raw millivolt signal from the sensor is outside the range -2100 to 2100 mV.
1. Verify all wiring connections, including connections in a junction box.
2. Check that the pH sensor is completely submerged in the process liquid.
3. Check the pH sensor for cleanliness. If the sensor look fouled of dirty, clean it. Refer to the sensor instruction manual
for cleaning procedures.
15.2.7 No pH Soln GND
In the transmitter, the solution ground (Soln GND) terminal is connected to instrument common. Normally, unless the pH
sensor has a solution ground, the reference terminal must be jumpered to the solution ground terminal. HOWEVER, WHEN
THE pH SENSOR IS USED WITH A FREE CHLORINE SENSOR THIS CONNECTION IS NEVER MADE.
15.2.8 Sense Line Open
Most Rosemount Analytical sensors use a Pt100 or Pt1000 RTD in a three-wire configuration (see Figure 15-4). The in and
return leads connect the RTD to the measuring circuit in the transmitter. A third wire, called the sense line, is connected to
the return lead. The sense line allows the transmitter to correct for the resistance of the in and return leads and to correct
for changes in lead wire resistance with changes in ambient temperature.
1. Verify that all wiring connections are secure, including connections in a junction box.
2. Disconnect the RTD SENSE and RTD RETURN wires. Measure the resistance between the leads. It should be less
than 5Ω.
3. The transmitter can be operated with the sense line open. The measurement will be less accurate because the trans-
mitter can no longer compensate for lead wire resistance. However, if the sensor is to be used at approximately con-
stant ambient temperature, the lead wire resistance error can be eliminated by calibrating the sensor at the measure-
ment temperature. Errors caused by changes in ambient temperature cannot be eliminated. To make the warning mes-
sage disappear, connect the RTD SENSE and RETURN terminals with a jumper.
15.2.9 Need Factory Cal
This warning message means the transmitter requires factory calibration. Call the factory for assistance.
15.2.10 Ground >10% Off
This warning message means there is a problem with the analog circuitry. Call the factory for assistance.
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