Instrotech Hazardous Area Load Cell Application
This is an application note for using load cells in a hazardous area ig. near flammable gasses.
The loadcell and junction box are mounted in the hazardous area
The cables are all fed through barriers to prevent any high voltages or currents
A standard load cell transmitter or display can then be used in the safe area
Wiring
| Load Cell |
Junction Box |
Barrier Term |
Barrier Type |
Barrier Term |
Transmitter or Display |
| Hazardous Area |
|
Safe Area |
|
|
|
| No. 1 |
Cable screen |
|
|
|
|
| |
+ Exitation |
|
|
|
|
| |
-mV |
|
|
|
|
| |
+mV |
|
|
|
|
| |
- Exitation |
|
|
|
|
| No. 2 |
Cable screen
|
|
|
|
|
| |
+ Exitation |
|
|
|
|
| |
-mV |
|
|
|
|
| |
+mV |
|
|
|
|
| |
- Exitation |
|
|
|
|
| No. 3 |
Cable screen
|
|
|
|
|
| |
+ Exitation |
|
|
|
|
| |
-mV |
|
|
|
|
| |
+mV |
|
|
|
|
| |
- Exitation |
|
|
|
|
| |
+ Exitation |
3 |
761 Pac |
1 |
+ Exitation out |
| |
- Exitation |
4 |
|
2 |
- Exitation out |
| |
+ mV |
3 |
766 Pac |
1 |
+ mV input |
| |
- mV |
4 |
|
2 |
- mV input |
| |
+ Sense |
3 |
761 Pac |
1 |
+ Sense input |
| |
- Sense |
4 |
|
2 |
- Sense input |
| |
+mA output |
3 |
706 |
1 |
+mA output |
| |
-mA output |
4 |
|
2 |
-mA output |
Load Cells
Load cells should be certified for the type of hazardous area
Junction Box
- Each load cell is wired in parallel
- The + sense is connected to the + exitation
- The - sense is connected to the - exitation
Barrier
These are mounted in the safe area
Transmitter or Display
- Provides exitation to the loadcells
- Senses the actual exitation voltage at the junction box
- Amplifies the mV signal from the load cell
- Local display is required
- Output mA or Volts
|
