Page 222 - Instrumentation Reference Book 3E

206 Microprocessor-based and intelligent transmitters

hand-held terminal or from the control room, MTL 418, both of which are extremely accurate
making it possible to check the operation of a two-wire 420 mA transmitters. The outline per-
transmitter without leaving the control room. formance characteristics are set out in Table 13.1
and the MTL 418 transmitter itself is shown in
Note: It is important to appreciate that the Figure 13.6. The transmitters are designed for use
information given in the following sections has in hazardous areas and can be installed in zone 0
been summarized from the various published for use with sensors also installed in zone 0, as
descriptions and specifications. It is provided for defined by the IEC Standard 79-10. (Details of
guidance and therefore not only is it incomplete, these requirements are given in Chapter 33,
but it may also become out of date. Readers Section 33.3, of Part 4.)
should refer to current manufacturers' documen- The MTL 414 is a conventional transmitter,
tation before embarking on any application. requiring at least 12V d.c. at 20mA. It can be
used with the MTL 7878 + safety barrier or the
MTL 3041 isolating interface units, as shown in
13.5 Microprocessor-based and Figure 13.7. It can also be configured for input
intelligent temperature type, range, etc.. before or after installation. A
transmitters local intrinsically safe indicator, such as the MTL
634 or MTL 681/2 can be included in the loop,
Several companies manufacture transmitters of provided that the interface unit or barrier gives
this type but the units manufactured by MTL sufficient voltage at 20mA.
(see References) have been chosen as examples. The MTL 418 combines the versatility of the
There are two models, the MTL 414 and the MTL 414 with even greater accuracy and the

Table 13.1 Outline performance specifications for the MTL 414 and MTL 418 transmitters.
~ ~____
Accuracy (MTL 414) fO.l'%t of mV or ohm range
(MTL 418) f0.05'%) of mV or ohm range
Repeatability (MTL 414) f0.05'%~
(MTL 418) *0.035'%1
Supply voltage 12-42V d.c.
Analog output 4-20 mA
signal
Fault indication Selectable, output driven to 21 mA or 3.9 mA
Input isolation 500 V
Update time Less than 0.5 s

Hazardous area Safe area
MTL414
M T L 7 0 7 S
MTL787SP
MTL4707 or
VI
1-5V
-I
ov
Field configurator

Lf7l 20-35V dc
Figure 13.6 The MTL418 temperature transmitter in MTL3041
the surface mounting enclosure (cover removed) and the Figure13.7 installation of the MTL 414 transmitter, with
stem-mounted enclosure. Courtesy of Measurement a safety barrier or an isolator. Courtesy of Measurement
Technology Ltd. Technology Ltd.