Emerson 8800A, Product Manual

Page: 65 / 160

3-17
Operation
Figure 3-1. Example: The pulse output will maintain a 50 percent duty cycle for all frequencies
NOTE
The scaled pulse output is designed to operate between 0 and 10,000
Hz. The electronics will not accept a conversion factor that would result
in a pulse frequency outside that range. Determine the minimum
conversion factor value by dividing the upper range value (in units of
volume per second) by 10,000 Hz.
The best choice for this parameter depends on the required resolution,
the number of digits in the totalizer, the extent of range required, and
the maximum counter input frequency.
Direct (Shedding Frequency)
This mode provides the vortex shedding frequency as output. In this
mode, the software does not compensate the K-factor for effects such as
thermal expansion or differing mating pipe inside diameters. Scaled
pulse mode must be used to compensate the K-factor for thermal
expansion and mating pipe effects.
Pulse Output Test
Pulse Output Test is a fixed frequency mode test that checks the
integrity of the pulse loop. It tests that all connections are good and
that pulse output is running on the loop.
HART Output
Multidrop configuration refers to the connection of several flowmeters
to a single communications transmission line. Communication occurs
digitally between a HART-based communicator or control system and
the flowmeters. Multidrop mode automatically deactivates analog
output of the flowmeters. Using the HART communications protocol, up
to 15 transmitters can be connected on a single twisted pair of wires or
over leased phone lines.
The use of a multidrop installation requires consideration of the update
rate necessary from each transmitter, the combination of transmitter
models, and the length of the transmission line. Multidrop installations
are not recommended where intrinsic safety is a requirement.
Communication with the transmitters can be accomplished with
commercially available Bell 202 modems and a host implementing the
HART protocol. Each transmitter is identified by a unique address
(1-15) and responds to the commands defined in the HART protocol.
50% Duty Cycle
88
00-
0546
a
HART Comm. 1, 4, 3, 2, 1, 3
HART Comm. 1, 4, 3, 2, 2
HART Comm. 1, 4, 3, 3