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IronHorse GSD1 DC Drives User Manual – 2nd Edition, Revision B – 10/12/2018
o
peraTional
D
eSCripTion
: 0
To
10 vDC a
naloG
r
eferenCe
S
iGnal
To
GSD1
IronHorse GSD1 drives, though advertised to work with a 0 to 10 volt reference, exhibit an offset in
output response when used in this manner. With 0 to 10 VDC connected to the GSD1 drive, output
voltage is zero volts until the analog reference value reaches two volts, where the GSD1 drive output
voltage will begin to rise. As the analog reference voltage rises, the GSD1 drive output voltage rises in
proportion and linear to the reference. At five volts reference the GSD1 drive output is 50%, and at 10
volts reference the output is 100% of the expected voltage. Adjustments to min and max speed have
no effect on the observed behavior.
The installation of a 4.7kΩ resistor across Pot Hi (P2-1) and Pot Lo (P2-3) helps with GSD1 drive
output voltage, but is NOT a perfect solution. With the resistor installed, GSD1 drive output voltage
is proportional to the lower reference voltage with a linear output response to midscale, where 1 to 5
volts reference equals 10% to 50% output. The problem is that linearity suffers as reference voltage
increases. If the drive is linear from 1 to 5 volts then output voltage is low at the top, where 10 volts
reference equals roughly 90% output. If adjustments are made to provide 100% output at the top,
then the drive ignores the falling reference voltage and runs fast at midscale, where 5 volts reference
equals 55% output.
All GSD1 drives have some dead band built into the speed pot circuit which, when a speed pot is used,
can be tuned out using the MIN trim pot. The physical connection of a speed pot also provides a
current path so that the MIN trim pot is active in the circuit. When using a reference signal connected
+Signal to Wiper and -Signal to Pot Lo, the current path for the MIN trim pot is lost and therefore no
longer in the circuit; thus the need for a 4.7–5 kΩ resistor from Pot Hi to Pot Lo.
With a 0–10 VDC reference signal input, and with the MIN trim pot active, the MIN trim pot can be
turned up to reduce or eliminate the dead band in the bottom end of the signal. However, this also
has the effect of shifting the reference signal to effectively be a 2–12 VDC signal. The top of the
reference (10–12 VDC) is ignored and the drive response becomes non-linear.
For most applications this is not an issue, as most do not operate in the bottom or top 20% of
reference signal / speed range. However, for those applications that do, another fix is to scale the
reference signal at the source to keep the effective reference signal always in the 0–10 VDC range.
Changing from a 0–10 to a 0–8 VDC signal at the source, and turning up the MIN trim pot ~2V to offset
dead band at the bottom, will operate the motor from 0–100% speed with a more linear response.
There is NO signal conditioning solution for the performance issue described in the GSD1 drive.
