Heinrichs Messtechnik
Installation and Operation Manual PITe
Page 15 of 22
The electrodes and measuring electronic are referenced to the potential of the functional earth FE of
the sensor. FE is not connected to PE, but may be connected in the sensor junction box if wished. If
ground disks (earthing rings) are used for grounding purposes, then these must be connected to the
functional earth FE.
Since the sensor and transmitter are mounted separ
e
tely, the outer shield of the connecting cable
must be connected to the transmitter housing via the cable gland and has PE potential. The inner
shields of the electrode and exciter wires are connected to FE inside the junction box of the sensor
and sowith to the ground (Gnd) of the transmitters electronic.
8.3 Cathode protective units
When using a cathode protective unit to avoid corrosion, thus putting a voltage to the tube wall, the
unit must be connected to terminal FE. The transmitter electronic, control panel and internal switches
are also all referenced to the FE potential.
Warning
According to EN 50178:1997 all electrical circuits with ”protective safety isolation”
which do not possess contact protection must observe the following maximum
voltages:
Maximum AC voltage (effective value) 25 VRMS
Maximum DC voltage 60 V
It is strictly forbidden to connect FE to a higher voltage!
8.4 Zero point calibration
To ensure precise measurements are obtained, zero point calibration is essential the first time the
device is put into operation and before any regular operations is carried out. To perform a zero point
calibration, the sensor head must be inserted approx. 40mm into the medium to be measured (see
section 7.1.2 “Immersion depth of PITe-*** in the pipe” on page 13
The zero calibration procedure is as follows:
-
Install the sensor as described in the manufacturer’s instructions.
-
Ensure that the sensor head is completely covered with fluid and that there are no gas
bubbles in the pipe around the sensor head.
-
Define the process conditions such as pressure, temperature and density.
-
Close a potential shut-off device behind the sensor.
-
Turn on the transmitter and ensure that sufficient time is allowed for the electronics to warm
up (20 minutes as a general rule).
-
Initiate the Zero point calibration sequence over the transmitter in accordance with the
appropriate transmitter-operating manual.
Allowing fluid to flow through the sensor during the zero calibration procedure will skew the zero point
and result in false future readings.
9 Startup conditions
The device is not subject to specific startup conditions. However, pressure surges should be avoided.
To ensure the transmitter correctly calculates the measured volume flow velocity, it is essential to
ensure that during commissioning of the PITe series of sensors, the installation requirements,
regarding position and mounting depth, are correctly adhered to.
