Thermo Fisher Scientific ECFP21A1A1 Differential pH Sensor - Manual (Page 15)

www.thermofisher.com
Temperature Span
Disconnect the BLACK and YELLOW sensor wires from the analyzer. Use an ohmmeter to measure the
resistance between the BLACK and YELLOW wires. The meter should measure a resistance
corresponding to the sensor temperature as outlined in the following table.
Sensor Temperature 5C 15C 25C 35C 45C
Thermistor Resistance 630 Ω 430 Ω 300 Ω 215 Ω 155 Ω
If the measured resistance is within 10 to 20 ohms of the expected value, the element should be
satisfactory. If not, please consult the factory.
pH Offset Test
1. Disconnect the RED and GREEN sensor wires from the analyzer terminal block while leaving the
other wires connected. Connect the (+) lead of a millivolt meter to the RED wire and the (-) lead
of the millivolt meter to the GREEN wire.
2. Put the sensor in 7 pH buffer. Stir the sensor for 10 to 15 seconds and then allow the sensor to
stabilize in solution for about 2 minutes. The meter should read 0.0mV +/- 50 mV. If the reading
is higher or lower than specified, replace the salt bridge and filling solution and try again. If on
the second attempt the offset does not meet specification, replace the sensor.
pH Span Test
If the RED and GREEN wires have already been disconnected to run the offset test, skip step 1.
1. Disconnect the RED and GREEN sensor wires from the analyzer terminal block while leaving the
other wires connected. Connect the (+) lead of a millivolt meter to the RED wire and the (-) lead
of the millivolt meter to the GREEN wire.
2. Rinse the sensor in clean water. Put the sensor in 4 pH buffer. Stir the sensor for 10 to 15
seconds and then allow the sensor to stabilize in solution for about 2 minutes. The meter should
read a change of at least 150mV from the offset reading. For example, if the offset is +20mV the
reading in 4 pH buffer should be at least 170mV.
After testing offset and span, the RED and GREEN wires should be reconnected to the analyzer terminal
block.
Sensor Power Test
If the sensor does not respond with any reasonable millivolt signal in the offset and span tests, it may be
worthwhile to verify that power is being supplied to the sensor from the analyzer. To do this, connect a
voltmeter from the BLACK lead to the WHITE lead (It is not necessary to disconnect the wires from the
terminal block). The meter should read –5 VDC +/- 0.3 VDC. If the voltage is low, disconnect the white
wire from the terminal block and measure the voltage on the terminal block. If the voltage comes back
into specification there is a defect in the sensor that is loading down the analyzer. If the voltage remains
low then the analyzer may be defective.
If the sensor passes the temperature, offset, span and power tests but the analyzer is not displaying the
correct values, the analyzer may be defective.
pH SENSOR SPARE PARTS & ACCESSORIES
5.1 Reference Cell Replacements
Description
• 01X211270 - Reference Cell Filling Solution (500 ml)