How many instruments can follow the master command from one Eurotherm 2400 SST Master instrument --
This is also referred to as the PDSIO Mode 4 Retransmission capability.
The SST setpoint retransmission allows a 2400 controller to deliver a master setpoint to a number of slave 2200 or 2400 controllers. In programmer applications the 'holdback' function in the slave controller can be used to 'freeze" the master setpoint program.
The questions are:
1. How many slaves can be connected?
2. When can holdback be used?
Basic rules:
1. The master must be a 2400 controller.
2. The slaves can be 2200 or 2400 controllers.
3. Holdback is only available with a 2400 slave. "Holdback" is a customer setting which halts the ramp/dwell program while waiting for the sluggish zone to catch up.
4. Holdback in a 2400 master is enabled or disabled in the configuration level by setting the PDSIO module Func as follows: SP.op: Setpoint retransmission with holdback Sp.nH: Setpoint retransmission with no holdback.
5. Holdback in a 2400 slave is disabled by setting the parameter Hb.tY in the SP list to OFF.
FANOUT RULES
1. Without Holdback Function
Up to five 2200 or 2400 slaves can be connected in series to a 2400 PDSIO output communications board (called a M7 board which is field configured as a TS -- transmit setpoint board).
Holdback must be disabled in all 2400 slaves.
| 2400 Master | Slave 1 | Slave 2 | Slave 3 | Slave 4 | Slave 5 | |||||
2. With Holdback Function
Up to three 2400 slaves can be connected in series to a 2400 PDSIO output.
| 2400 Master | Slave 1 | Slave 2 | Slave 3 |
3. Without Holdback up to three chains can be connected in parallel
| 2400 Master | Slave 1 | Slave 6 | Slave 11 | |||
| Slave 2 | Slave 7 | Slave 12 | ||||
| Slave 3 | Slave 8 | Slave 13 | ||||
| Slave 4 | Slave 9 | Slave 14 | ||||
| Slave 5 | Slave 10 | Slave 15 | ||||
| 250 ohm | 250 ohm | 250 ohm |
When the number of slaves is the same in each chain, wire a 250 ohm resistor in series with each chain to ensure current sharing. The three chains of instruments are wired in parallel to the PDSIO Master output.
| 2400 Master | Slave 1 | Slave 5 | ||
| Slave 2 | Slave 6 | |||
| Slave 3 | Slave 7 | |||
| Slave 4 | 250 ohm | |||
| 250 ohm | 250 ohm |
When the number of slaves in each chain cannot be the same, fit additional 250 ohm resistors in place of missing slaves. (Max of 1 extra per chain)
4. Two PDSIO output communications boards (2 of the M7 boards) can be installed in the 2408 & 2404 controllers allowing up to 30 Slaves
| 2400 Master |
| Output 1 |
| Output 2 |
Up to 15 slaves on each PDSIO Master output.
5. Each 2408 or 2404 slave can retransmit its input as an output to a further set of PDSIO slaves. There will however be a transmission delay of about 2 seconds.
| 2400 Master | Slave 1 | Slave 6 | Slave 11 | |||
| Slave 2 | Slave 7 | Slave 12 | ||||
| Slave 3 | Slave 8 | Slave 13 | ||||
| Slave 4 | Slave 9 | Slave 14 | ||||
| Slave 5 | Slave 10 | Slave15 | ||||
| 250 ohm | 250 ohm | 250 ohm |
A 2408 or 2404 slave can retransmit its input as a master output to a further set of slaves.
When the number of slaves is the same in each chain, wire a 250 ohm resister in series with each chain to ensure current sharing.
Acknowledgments:
To Arthur Trewhella , John Houldsworth, Chris Williams and Paul Cutler -- thank you each for your comments.