Ametek Z-tron IV, Инструкция по установке и эксплуатации

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Troubleshooting
23
5.3 Testing Sensing Element
With level below the sensing element:
1. Disconnect remote cable, if applicable.
2. Use an analog ohmmeter¹ that is set to the R x 1K ohm
scale. Measure the resistances between each pair of
sensing element connections. See Figure 5-1. Record
values in Table.
a. If the process material is conductive, it is normal to
measure some resistance between sensing element
connections. The lowest permissible resistance values
are:
Center Conductor to Housing 1500 ohms.
Center Conductor to Cote Shield 750 ohms.
Cote Shield to Housing 750 ohms.
3. Clean sensing element and repeat resistance
measurements with the sensing element external to the
vessel.
a. A clean sensing element should measure an open
circuit on all resistance tests.
b. If resistance values increase to an open circuit the
resistance was installation or coating related. The
most common causes are:
i. Cote Shield element does not extend sufficiently
into the vessel. Verify the CoteShield element
extends at least 2” into the vessel and past wall
build-up.
ii. Extremely conductive coating on the sensing
element. This may require changing the sensing
element or electronics. Contact the factory for
recommendations.
iii. Sensing element is touching vessel. A resistance
reading of less than 10 ohms to ground (sensing
element housing or tank) is usually due to a metal-
to- metal short circuit. Verify that the sensing
element is not touching any vessel structure.
c. If the sensing element still shows resistance between
terminals of less than 10K ohms, it is possible that
moisture is present internal to the sensing element. It
may be possible to dry the sensing element until the
resistance increases to a value in excess of 10K ohms.
However this is an indication the integrity of the
sensing element has been compromised. Contact the
factory for recommendations.
1
A digital ohmmeter will often produce a resistance
measurement that is higher than the actual value.