B800-00-880 Issue A
Page 40
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Installation
3.7.7
Multi-drop operation
Using multi-drop mode, a single computer system can communicate with more than one nEXT pump. Each nEXT pump
must be assigned its own individual address before it can be fitted into a multi-drop system. The command to assign
the multi-drop address is sent in standard nEXT message format (as detailed in
.
The message protocol in multi-drop mode is marginally different to that described for serial messages in single pump
systems. The main differences in multi-drop message protocol are detailed below:
All multi-drop commands, queries or replies have the first character #.
All commands, queries and replies contain a header containing the address of the node that the message is
to, followed by the address of the node that the message is from.
There is a delimiter character: (colon) which separates the two multi-drop addresses in the header.
The remainder of the message (command, query or reply) follows the same protocol as already described for
single pump systems.
The wild card address 99 is very useful and means ‘any’ node.
After a nEXT pump has been assigned a multi-drop address, it will ignore any messages in the format for single pumps.
An individual nEXT pump will remain silent and ignore all command messages unless the multi-drop address matches
its own address.
3.8
Vent options, vent valve connection and control
CAUTION
If the pump is vented when it is at full rotational speed and the rate of pressure rise is too high, the pump could
be damaged and its life may be reduced. We therefore recommend that either the rate of pressure rise is limited
(refer to
) or that the vent valve is only opened after the nEXT pump speed has fallen to 50% of full
rotational speed.
To maintain the cleanliness of your vacuum system, we recommend that, whenever you switch the pump off, you
vent the pump (or vacuum system) when the speed of the nEXT pump is between full rotational speed and 50% of full
rotational speed. Over this speed range, the rotor spins fast enough to suppress any backstreaming of hydrocarbon
oil from your backing pump.
Do not connect the vent-valve to the backing pipeline, this may lead to contamination. Connect the inlet of the vent-
valve to the vent gas supply (refer to
for the vent gas specification).
Venting may be accomplished by using one of the following methods described in
to
3.8.1
Manual vent valve
A manual vent-valve is supplied with the nEXT pump. It is not possible to accurately control the rate of pressure rise
using the manual vent valve so take care not to open it too quickly. We recommend that you open the manual vent-
valve only after the pump speed has fallen to 50% of full rotational speed.
3.8.2
TAV5 or TAV6 solenoid vent valve
The TAV5 and TAV6 solenoid valves can be purchased as accessories – see
. The solenoid valves can be
used in the following ways:
Use a TAV5 or TAV6 solenoid valve in place of the manual vent valve on the pump
Use a TAV5 or TAV6 solenoid valve connected to a convenient flange on your vacuum system
Summary of Contents for nEXT240
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