Measurement Computing BTH-1208LS-OEM - Manual (Page 14)

BTH-1208LS-OEM User's Guide Functional Details
14
Signal connections
Analog input
You can connect up to eight single-ended analog input connections ( CH0 to CH7 ) or four differential
connections ( CH0H/CH0L to CH3H/CH3L ) on connector J1.
Single-ended configuration
When configured for single-ended input mode, eight analog input channels are available. Each analog input has
11-bit resolution (due to restrictions imposed by the A/D converter) and offers a ±10 V analog input range.
The input signal is referenced to signal ground ( AGND ), and is delivered through two wires:
 Connect the wire carrying the signal to be measured to
CHx .
 Connect the second wire to
AGND .
Single-ended measurements using differential channels
To perform a single-ended measurement using differential channels, connect the signal to the CHxH input, and
ground the associated CHxL input.
Differential configuration
When the analog input channels are configured for differential input mode, four analog input channels are
available. A low-noise precision programmable gain amplifier (PGA) is available on differential channels. Each
analog input has 12-bit resolution and offers software-selectable analog input ranges of ±20 V, ±10 V, ±5 V, ±4
V, ±2.5 V, ±2.0 V, ±1.25 V, and ±1.0 V.
In differential mode, the input signal is measured with respect to the low input. The input signal is delivered
through three wires:
 Connect the wire carrying the signal to be measured to CHxH .
 Connect the wire carrying the reference signal to CHxL .
 Connect the third wire to AGND .
In differential mode, the following two requirements must be met for linear operation:
 Any analog input must remain in the −10 V to 20 V range with respect to ground at all times.
 The maximum differential voltage on any analog input pair must remain within the selected voltage range.
Channel gain queue
The channel gain queue feature allows you to set up a scan sequence with a unique per-channel gain setting and
channel sequence. The gain settings are stored in a channel-gain queue list that is written to local memory on
the device.
The channel-gain queue list can contain up to up to 8 elements in single-ended mode or four elements in
differential mode. The elements must be unique and listed in ascending order. An example of a three-element
list is shown in the table below.
Sample channel gain queue list
Element Channel Range
0 CH0 BIP10V
1 CH2 BIP5V
2 CH3 BIP10V
When a scan begins with the gain queue enabled, the BTH-1208LS-OEM reads the first element, sets the
appropriate channel number and range, and then acquires a sample. The properties of the next element are then
retrieved, and another sample is acquired. This sequence continues until all elements in the gain queue have
been selected. When the end of the channel list is detected, the sequence returns to the first element in the list.
This sequence repeats until the specified number of samples is acquired.