A1 29 DTR.APC.APR.ALW.03
(ENG)
9.2. Electrical connections for APC..., APR...
The APC..., APR... transmitters are to be connected as shown in fig. 2a – 2d.
In APC..., APR... transmitters, a 240 resistor is permanently fitted in series in the transmitter’s current
circuit and blocked up with jumper between <SIGNAL –> and <TEST –> as shown in fig.2a and 2b.
When the resistance in the current loop is lower than 240 it is necessary to jumper disassemble to
Hart communication.
9.3. Protection from excess voltage
9.3.1. The transmitters may be in danger from excess voltage caused by connection faults or atmospheric
electrical discharge.
Protection from excess voltage between the wires of the transmission line is provided by TVS diodes installed in
all types of transmitter (see the table, column 2).
9.3.2. In order to protect against excess voltage between the transmission line and the casing or earth (not
prevented by the diodes connected between the transmission wires), additional protection is provided in the
form of plasma surge arresters (see the table, column 3).
Also external protective devices may be used, e.g. the UZ-2 Aplisens system, or others. When the transmission
lines are long, it is advantageous to use one protective device near the transmitter (or inside it), and another near
entry points to other devices used in conjunction with it.
Internal protection of transmitters:
1 2 3
Type of
transmitter
Protection between wires (TVS
diodes) – permitted voltage
Protection between wires and earth and/or casing –
type of protection, permitted voltage
APC..., APR...
68V DC
(39V DC for Exi and MID version)
Plasma surge arresters - 230V DC
(Not applicable to Exi, Exd, MID version).
9.3.3. The voltage in the protective elements must not exceed the maximum permitted values given in columns
2 and 3 of the table.
The insulation test voltages (500V AC or 750V DC) given in 5.1.1 refer to transmitters plasma surge
arresters - such protection is not used in Exi versions of transmitters.
9.4. Earthing
The transmitters are fitted with internal and external earth terminals.
10. SETTING AND REGULATION
APC..., APR... transmitters are factory calibrated to the range stated in the order or to the basic range.
After installation, the transmitter’s zero-point may move and require adjustment.
This applies particularly in cases where the measurement range is small, where the impulse lines are filled with
a separating liquid or where APC..., APR... transmitters are used with remote diaphragm seals.
10.1. Transmitter Range, Basic Range. Definitions
10.1.1. The maximum range of pressure, or differential pressure, which the transmitter can measure is called
the “basic range” (for specifications of basic ranges see section 5.2.1, 5.3.1, 5.3.2, 5.4.1, 5.5.1).
The width of the basic range is the difference between the upper and lower limits of the basic range.
The internal characteristic conversion curve for the basic range is coded in the transmitter’s memory.
This is the reference curve used when making any adjustments which affect the transmitter’s output signal.
10.1.2. When the transmitter is in use the term “set range” is used. The set range is the range whose lower
end-point corresponds to an output current of 4mA and whose upper end-point corresponds to a current of
20mA (or 20mA and 4mA respectively when the conversion curve is inverted).
The set range may cover the whole of the basic range or only a part of it.
The width of the set range is the difference between its upper and lower end-points.
The transmitter may be set to any range within the basic range of pressure values, subject to the restrictions set
out in the table in section 5.2.1, 5.3.1, 5.3.2, 5.4.1, and 5.5.1.
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