BK Precision 1794, Instruction Manual

4.4

Positive or negative voltage can be obtained from this supply by grounding either
one of the output terminals or one end of the load.  Always use two leads to connect
load to the supply, regardless of where the setup is grounded. This will eliminate
any possibility of the output current return paths through the power source ground
which would damage the line cord plug. This supply can also be operated upto
±300V DC above ground, if neither output terminal is grounded.

4.5

REMOTE SENSING :
Warning :

Do  not  Operate  the  Unit  in 'REMOTE SENSE' mode without
ensuring proper 'REMOTE/ 4 TERMINAL' Connections. Serious
Damage to Unit or Equipment under test could result.

Remote sensing is used to maintain good regulation at the load and reduce the
degradation of regulation which could occur due to the voltage drop in the leads
betweeen the power supply and the load. Remote sensing is accomplished by
connnecting the load to remote sense terminals  on the front panel. The leads from
the sensing( +S and -S) terminals to the load will carry much less current than the
load leads and it is not required that these leads be as heavy as the load leads.
However, they must be twisted or shielded to minimize noise pickup.

For  reasonable  lengths  of  load  leads, remote sensing greatly improves the
performance of  the supply.  However, if  the load is located at a considerable
distance  from  the  supply,  added  precautions  must  be observed to obtain
satisfactory operation. Notice that the voltage in the load leads subtracts directly
from  the  available output voltage and also reduces the amplitude of the feedback
error signals  that  are  developed  within the unit. Because of these factors, it is
recommended that the drop in each load lead does not exceed 0.5Volts.

  NOTE :

Due  to  the  voltage  drop  in  load leads, it may be necessary to
readjust  the current limit in the remote sensing mode.

Observance of the precautions in para. 4.8 and 4.9 will result in a low dc output
impedance at the load. However, another factor that must be considered is the
inductance of long leads.This causes a high ac impedance and could affect the
stability of the feed back loop seriously enough to cause oscillations. If this is the
case, it is recommended that the following actions be taken:

a)

Adjust  R6  to remove oscillations, or to achieve best possible transient
response for given long load lead configuration.

b)

If performing  adjustment  in  step  (a)  above  does not remove oscillation,
disconn-ect  output  capacitor  C3  ( L1791-FP-CNT-0603 PCB ) and  connect
a capacitor having similar characteristics (approximately the  same capaci
tance, the same voltage rating or greater, and having good high frequency
characteristics) directly across load using short leads.
Readjust R6 as in step (a) above after making this change.

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