Kipp&Zonen UVS-E-T UV Radiometers - Manual (Page 10)

10
The formula for R
max
is:
R
max
= ([VT+] - 6 V) / 1.2 A
where [VT+] is the supply voltage and R
max
is the sum
of the total wire resistance and the internal resistance
of the power supply.
Example 1:
The supply voltage is 12 VDC. The internal resistance
of the power supply is 1
Ω (i.e. voltage drop of 1 V at 1
A load). Then the allowable total wire resistance (sum
of positive and negative supply wire) is 4
Ω.
Example 2:
To calculate the minimum voltage that is required for
correct operation of the radiometer with the standard
cable of 10 m length, the above equation has to be
reformulated as follows:
[VT+] = 1.2A
• R
tot
+ 6V
where R
tot
is the sum of the resistances (internal
resistance of the power supply and total wire
resistance). With the wire resistance of 0.15
Ω/m a total
wire resistance of 2 x 1.5
Ω = 3Ω for the standard 10 m
cable is obtained. With an internal resistance of 1
Ω
(power supply) the sum of the resistances is 4
Ω
(equals R
tot
). To compensate for the voltage drop over
the wires and power supply, the voltage supply [VT+]
must be at least 10.8V. Hence, with a power supply
(internal resistance 1
Ω) that provides at least 10.8V the
radiometer will operate correctly.