8

Why is there a 2 in front of some of these passive component parts?

enter image description here

apaderno
  • 107
  • 4
Bringle
  • 159
  • 6
  • 2
    Note that in some applications, the actual values of resistor/resistor pairs may not be critical, but their ratios is. – SteveSh Feb 27 '21 at 21:55

3 Answers3

32

Well, \$R_B\$ is defined as 1 MΩ and so \$2R_B\$ is 2 MΩ: -

enter image description here

Andy aka
  • 434,556
  • 28
  • 351
  • 777
  • 3
    Presumably it's done as \$2R_B\$, rather than \$R_C\$ with \$R_C=2MΩ\$ because the fact that one is twice the other is more important than the absolute value? Is there an obvious reason why there "seems" (from symmetry, if nothing else) to be a "missing" \$R_B\$ in the lower half? – TripeHound Feb 26 '21 at 09:55
  • 4
    @TripeHound yes, the lower resistor network is asymmetrical so that if the thermocouple became disconnected or broken, there is a means by which the monitoring circuit can detect this situation. – Andy aka Feb 26 '21 at 09:58
11

It means whatever value you choose for \$R_\mathrm B\$, use \$2\times R_\mathrm B\$ at that position. Eg \$R_\mathrm B\$ is \$1\ \mathrm{M\Omega}\$, \$2R_\mathrm B\$ is \$2\ \mathrm{M\Omega}\$.

Community
  • 1
Martin
  • 8,320
  • 1
  • 22
  • 30
7

It means that the 2RA resistor values are twice those of the RA values and similarly with the RB values.

If RA is 1 kΩ then the 2RA value is 2 kΩ.

Transistor
  • 168,990
  • 12
  • 186
  • 385