Instructions

UM-0085-B09 DT80 Range User Manual Page 75
RG
Derived Quantities
The DT80 can automatically compute various commonly used derived quantities such as differences, rates of change,
pulse widths and so on. These are calculated by including the appropriate channel option, as detailed below.
In each case the derived quantity is returned instead of the original reading.
Rates and Integrals
The following derived quantities are calculated based on the current and the previous channel reading.
Channel Option
Description
Formula
DF
Difference
Δx
DT
Time difference
Δt
RC
Rate of change
Δx / Δt
RS
Reading / time difference
x / Δt
IB
Integrate
( x – Δx / 2 ) Δt
The DF channel option returns the difference between the current and previous measurements; the DT option returns
the time difference and the
RC channel option combines the two to return the rate of change (Δx / Δt).
For example,
RA1S 1V &1V(DF,"DeltaV") &1V(DT,"DeltaT") &1V(RC,"RC~mV/s")
1V 29.4 mV
DeltaV 3.9 mV
DeltaT 00:00:00.992
RC 4.0 mV/s
In this case four channels are defined in the schedule. The first will measure a voltage and return the reading. The
second channel will compare the newly updated value of 1V to the value it had when the channel was last evaluated
(one second ago) and return the difference. Similarly the third and fourth channels will return the time difference (which
will in this case always be close to one second) and rate of change, respectively.
The
RS option is similar to RC except that the numerator is the actual reading, not the difference. This is intended for use
with channels where the reading is already a difference. In the following example the counter is reset after each reading
(using the R channel option), so the count reading is actually the number of counts since the last reading, so to calculate
counts per second the
RS option is used:
RA10S 3C(R,RS,"~counts/s")
Finally, the IB option is used to integrate a signal. It returns the area under a straight line connecting the current to the
previous reading. For example:
RA20S
1V(W) 2#I(W)
CALC("Power~W")=&1V*&"2#I"
&Power(IB,W,+=5CV)
5CV("Energy~J")
The above example will, every 20 seconds, first measure a voltage and a current. These are then multiplied to give the
instantaneous power in Watts, then integrated to give the energy used over the 20 second period. Finally, the energy
values are accumulated in channel variable 5CV to give the total energy used.
Edge Timing
A number of channel options are provided for reporting details relating to the timing of digital transitions (edges).
As with the rate and integral options, these derived quantities are calculated based solely on the current and the previous
channel readings.
The TOR and TOF options return the absolute date/time at which a last rising or falling edge occurred. If no edge has
occurred since the last reading then a "zero" date/time value (normally presented as 00:00:00.000,01/01/1989) is
returned.
The following options report the time interval between two edges:
• If a rising edge has occurred since the last reading on a channel, and another rising edge has occurred some
time previously, then the
TRR option returns the time interval between the two edges, otherwise it returns zero.
• If a rising edge has occurred since the last reading on a channel, and a falling edge has occurred some time
previously, then the TFR option returns the time interval between the two edges, otherwise it returns zero.