Faults
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BPD17 pH / Redox Monitor
Operating Guide
Input Cable
The choice of cable is important. Only polythene or PTFE cables are acceptable. Secondly, any
vibration or cable movement on a standard co-axial cable will give rise to fluctuations in the readings.
To prevent this a low noise cable must be employed. This type of cable can be identified as having a
black impregnated polythene layer which is exposed when the outer braid is separated for connection.
This must be completely removed at the terminations to avoid a possible short circuit between the
electrode and reference pair.
In all cases the screening braid must not be separated from the core conductor by more than 5mm in
order to avoid “hum” pickup.
Cables should be kept as short as possible and must be run separately (100mm separation typically)
from any power carrying cable.
Cable Length
The response of the instrument to a sudden change in the sensor input will be determined mainly by
the source resistance of the electrode and the length of the connection cable. For a typical pH
electrode of 1000M resistance, in combination with a typical cable, the time taken to settle to its new
value is about 0.5 seconds per metre of cable (depending on the cable capacitance).
Problems with Electrodes
The combination electrodes supplied by LTH are of low resistance and will be less affected by humidity
than other, high resistance systems. In any case, the connecting leads and cable connectors must be
kept dry, and the cable screen must not be allowed to come into contact with any earthed metal parts.
The glass bulb must be kept in a moist condition for correct operation. If the electrode is allowed to
dry out, it may be recovered by immersing in a saturated KCl solution or dilute acid for at least 24
hours before use.
Electrodes can be expected to last for at least one year under normal operating conditions before
replacement becomes necessary. However, operation at elevated temperatures or pressures, and the
presence of sulphides or ionic metals, will shorten the electrode life. If the electrode cannot be set up
against solutions or shows a sluggish response to changes in pH, it should be replaced.
Guarantee and Service
Products manufactured by LTH Electronics Ltd are guaranteed against faulty workmanship and
materials for a period of three years from the date of despatch, except for finished goods not of LTH
manufacture, which are subject to a separate agreement.
All sensors made by LTH Electronics Ltd are thoroughly tested to their published specification before
despatch. As LTH have no control over the conditions in which their sensors are used, no further
guarantee is given, although any complaints concerning their operation will be carefully investigated.
Goods for attention under guarantee (unless otherwise agreed) must be returned to the factory
carriage paid and, if accepted for free repair, will be returned to the customer’s address free of charge.
Arrangements can also be made for repair on site, in which case a charge may be made for the
engineer’s time and expenses.
If any services other than those covered by the guarantee are required, please contact LTH direct.
N.B. Overseas users should contact their LTH nominated representative. Special arrangements will be
made in individual cases for goods returned from overseas.
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