EDR to 20240 Connection
Background
The 20240 (EMD) is a module that historically is used for ZZZZ compliance monitoring. Since it has a RS-485 slave port, it can also be used as a generic sensor to modbus translator.
In a typical scenario, a 20240 and a few sensors could be added to an old annunciator panel (e.g. TTD or DD-40) to allow the EDR to send the sensor values remotely.
The 20240 can be connected to the following number of sensors:
- Analog (e.g. pressure sensor): 5 - 7
- Thermocouple (Type K): 6
- Thermistor: 0 - 2
- Digital Inputs: 2
Note that the thermistor inputs can be used for thermistors or analog.
Wiring
- Wire fused power into pins 4,5 of the 20240.
- For a typical loop powered pressure sensor, wire the power wire into a +12v pin (21, 17, 44) and the signal wire into the input (pin 20, 23, 45, 42, or 19).
- For thermocouples wire into pins 24-35 depending on input number
- For a digital input wire into 39 or 41 with the other side of the switch to ground (40)
- For a thermistor wire between 36-37 or 38-37
- Wire the modbus A,B wire back to the EDR master port. In most cases the wires will then daisy-chain to the annunciator as shown in the diagram below. Since in this case wires are coming in and out of the 7,8,9 plug the termination switch will be off (in) as shown. In the less common case where the 20240 is at the end of the chain the termination will be on (out).
Input Numbering
The pins map to the input numbers with the following table.
| Input | Pin |
|---|---|
| Thermocouple 1 | 24, 25 |
| Thermocouple 2 | 26, 27 |
| Thermocouple 3 | 28, 29 |
| Thermocouple 4 | 30, 31 |
| Thermocouple 5 | 32, 33 |
| Thermocouple 6 | 34, 35 |
| Thermistor 1 | 36* |
| Thermistor 2 | 38* |
| Analog 1 | 20 |
| Analog 2 | 23 |
| Analog 3 | 45 |
| Analog 4 | 42 |
| Analog 5 | 19 |
| Analog 6 | 36* |
| Analog 7 | 38* |
| Digital in 1 | 39 |
| Digital in 2 | 41 |
- Pins 36 and 38 can be used as thermistor OR analog input (if adding a resistor), see below
Thermistor input note
Pins 36 and 38 can each be used as a thermistor or an analog input (but not both). Using as an analog input requires adding a 249 ohm resistor to ground. This would only be done if needing more than 5 analog inputs.
