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Appendices
218 UDA2182 Universal Dual Analyzer Product Manual January 2009
15.8 Appendix G – Noise Testing, Dissolved Oxygen Application
Hints for Reducing Noise
Specifications for proper operation of Honeywell dissolved oxygen (DO) probes demand
that the alternating current (AC) voltage signal (noise) between anode and shield
connections and cathode and shield connections be less than 1 mV AC.
While it is your responsibility to assure that this specification is met, the following are
some hints that have been successful in reducing these signals to the required value in a
variety of installations.
1.
First eliminate external connections as a source of excess AC noise.
2.
After installation of all wiring, use a digital voltmeter to check the following
voltages:
Anode - Shield 1.2 to 2.0 VDC depending on oxygen level
less than 1 mV AC. In low ppb measurements, this
value may be zero.
Cathode - Shield < 1 mV DC
less than 1 mV AC
3.
Any readings greater than the limits shown above indicate electrical noise that should
be corrected.
4.
Systematically remove external connections to the Analyzer, noting if the voltage
drops within the acceptable limit.
5.
If a noise source is identified, improved shielding, grounding or re-routing of that
cable may be required. (In attempting to reduce AC noise, do not ground the shield as
this shunt filtering is designed to reduce electromagnetic interferences {EMC}.)
6. If the measured voltages are greater than procedures states, one at a time remove an
external connection (ex., isolated outputs and relays) and re-measure the AC signal. If
the AC signal has decreased after disconnecting one of these connections, then this
was the source of the noise.
7.
If the noise remains at a value greater than 1 mV AC after disconnecting all external
connections described in step 1, disconnect the shield wire from Terminal 7 and
connect it to instrument ground inside the case.
8. If the noise remains at a value greater than 1 mV AC after performing step 2,
reconnect the shield wire to Terminal 7 and connect an additional (jumper) wire from
ground to the shield connection, Terminal 7.
If these steps fail to reduce the Anode-Shield and Cathode-Shield AC signals to the
specified 1mV AC or less, obtain an isolated transformer and power the analyzer from
that.