Introduction; Pcb Functions; Junction Box Mounting; Connection Of Load Cells And Terminal - Mettler Toledo Precision Junction Box AJB Serie Manual De Instalación

1 Introduction

Precision Junction Boxes are intended to connect analog load cells with nominal bridge resistances from 120 to 4000 ohms and allow
very precise shift adjustment by selecting precision resistors via two hex-step switches.
1.1

PCB Functions

INPUT
LC1-LCn
EN 60079-0 2012 +A11;
EN 60079-11 2012
AUX
CUT for 1000R
Cut for 2000R (only AJB541M and AJB540L)
SW

2 Junction Box Mounting

Mount the Junction Box in a location where it will be protected from rain, flooding and direct wash-down. Do not mount the box in direct
sunlight or to a heated or cooled surface e.g. the side of a heated tank.

3 Connection of Load Cells and Terminal

• Connect all cables to the Junction Box(es)
• Set all Shift Adjustment Switches to 80 (x16=8, x1=0)

4 Multiple Junction Box Connection

If connecting multiple boxes via AUS, refer to the installation manual for cable requirements and shift adjustment procedure.

5 Pre-Calibration

Coarsely calibrate the scale before making further adjustments to assure stable signal conditions. Use known test weight or CalFee™.

6 Height-Adjustment

When a scale with 4 or more load cells is first installed, inevitably it will "rock", so the load cell assemblies must be adjusted in height
until all carry a portion of the dead load. Otherwise the scale may be non-repeatable, it may be impossible to get a proper calibration and,
in the worst case, load cell(s) may be damaged.
6.1

Floor Scales

Floor Scales typically have adjustable feet. Find the rocking corner and adjust the height until rock is eliminated. Lift up on each corner
(using a bar if necessary) to roughly gauge the load distribution; adjust foot height again if necessary.

6.2 Tank and Hopper Scales

Tank and Hopper Scales are usually constructed using weigh modules and height adjustment is typically done by adding shims. Proceed
as described for Floor Scales above, adding shims as required above or below the weigh module. If this method is not practical, e.g., with
high capacity tank, refer to the height adjustment procedure in the Installation Manual. Ideally Tank and Hopper Scales would be placed
on structures that are equally stiff at all support points; if this is not the case, care must be taken that the load cells are not overloaded at
scale capacity, refer to the Installation & Service Manual for more details.
30766399D Precision Junction Box
Connection terminal strip for home run cable from terminal – always 6 wire cable
plus a shield wire
Connection terminal strip for 4 or 6 load cells, depending on the junction box
EN 60079-0 2012 +A11; EN 60079-11 2012
EN 60079-15 2010 ; EN 60079-31 2009
Connection terminal strip for a second junction box – always 6 wire connection
plus shield wire
Cut all wires for shift adjusting ≥1kΩ load cells
Cut all these resistors for shift adjusting ≥2kΩ load cells
NOTE: 1000R wires need to be cut as well
Shift Adjusting Switches
-00 lowest signal
-FF highest signal
X16 coarse, x1 fine
3
Introduction