Gradient Amplifier ------------------ .. figure:: /images/peripherals/grad/amp_front.jpg :width: 100% :align: center Gradient Amplifier Module Front .. figure:: /images/peripherals/grad/amp_rear.jpg :width: 100% :align: center Gradient Amplifier Module Rear The Gradient Amplifier module can be used with Kāhu to drive a single gradient coil with a controlled-current output of up to 10 A. Connections ^^^^^^^^^^^ On front of the module you will find the BNC connector for attaching the gradient control signal from Kāhu. Additionally you will find the on/off power switch and the indicator lights. The top light will illuminate green when the module is powered on, while the bottom light will illuminate blue when the amplifier is enabled by the interlock or will illuminate red to indicate an error. .. figure:: /images/peripherals/grad/front_labelled.png :width: 100% :align: center Front Controls, Connectors & Indicators The ports for the 24 V power input, high power gradient output and interlock can be found at the rear of the module. .. figure:: /images/peripherals/grad/back_labelled.png :width: 100% :align: center Rear Connectors Setup Guide ^^^^^^^^^^^ This section will guide you through the steps required to connect and power the Gradient Amplifier Module with the Kāhu Spectrometer. .. warning:: **Ensure the Gradient Amplifier module is OFF during Kāhu power up and shutdown and when changing RF connections.** **Step 1 - Rear Cable Connections** Begin by arranging the modules as shown in the image below with the Kāhu Spectrometer placed on top of the drive module(s). Note that the image below also shows the Shim module in the stack-up. This module is not required to run the Gradient amplifier, and if it is not being used simply place the Gradient amplifier module to the side of Kāhu. .. figure:: /images/peripherals/shim/stacked.jpg :width: 100% :align: center Kāhu, Shim & Gradient Amplifier modules stacked Complete the initial rear Kāhu connections as explained in the Kāhu Hardware :ref:`setup:Connections` section. Connect the 24V, 160 W external power brick to the Gradient amplifier (do not turn amplifier on). .. figure:: /images/peripherals/grad/power.jpg :width: 100% :align: center Power supply: 24V, 160W Next, using the provided cable, fasten the 4-pin interlock connector to the 'I' port on the amplifier module using the H2.0 driver tool provided. **Take care not to overtighten**. Connect the other end of the cable to the i-lock port on Kāhu. .. figure:: /images/peripherals/grad/interlock.jpg :width: 80% :align: center Interlock cable connection Lastly, connect the high power gradient output port (labelled *Out* on the module) to your gradient coil. The mating connector required is the `MMI-M1PG02S72 `_ and the pinout on the module is as follows: .. list-table:: :header-rows: 1 :width: 50% :widths: 70 200 :align: center * - Pin No. - Description * - 1 - I+ * - 2 - I- .. figure:: /images/peripherals/grad/HP_grad_conn.png :width: 30% :align: center High power gradient output pinout .. note:: **To avoid damage, take care to correctly orientate the connector by aligning the red markings on the connector and port.** **Step 2 - Front Cable Connections** Connect a gradient control output from Kāhu to the low power gradient input BNC connector on the Gradient Amplifier module. The example below shows Gradient port 3 from Kāhu connected to the module. .. figure:: /images/peripherals/grad/grad_conn.jpg :width: 80% :align: center Low power gradient connection **Step 3 - Power up** Power on Kāhu and establish a network connection from your PC. Once Kāhu power up has finished, you can power on the Gradient Amplifier with the power switch. Specifications ^^^^^^^^^^^^^^ General """"""" .. list-table:: :header-rows: 0 :width: 100% :widths: 70 200 :align: center * - Power Supply - 24 V, 160 W * - Dimensions - 150 x 200 x 65 mm (Width x Depth x Height) * - Weight - 2 kg .. todo:: Kerry check dimensions and weight Amplifier """"""""" .. list-table:: :header-rows: 0 :width: 100% :widths: 70 200 :align: center * - Current output Range - ±10 A * - Voltage output Range - ±15 V * - Input Voltage Range - ±10 V * - Load Resistance - 0.5 - 1 Ω, **1 Ω Nominal** * - Transconductance Gain - 1.0 A/V * - Maximum Overall Duty Cycle (±10 A output) - 25% [#techf1]_ [#techf2]_ * - Maximum Continuous Pulse Width (±10 A output) - 10 seconds [#techf1]_ .. [#techf1] Exceeding these limits may cause the over-temperature cutout to activate, disabling the amplifier. .. [#techf2] The amplifier may drive up to ±2.5 A indefinitely. Detailed Description ^^^^^^^^^^^^^^^^^^^^ Amplifier """"""""" The amplifier is a voltage controlled current source design. The output current will be proportional to the input voltage according to the following transfer function: .. math:: I_{out} = 1.0 * V_{in} Interlock """"""""" The interlock is a 5 V TTL input, which is used to enable the amplifier module when a pulse sequence is active, and disable it when in standby. The part number for the mating connector used in the interlock cable (on the amplifier side) is the `M80-4140498 `_. The pinout of the 'I' port on the module is: .. list-table:: :header-rows: 1 :width: 50% :widths: 70 200 :align: center * - Pin No. - Description * - 1, 2, 3 - GND * - 4 - Interlock input .. figure:: /images/peripherals/grad/interlock_conn.png :width: 40% :align: center Interlock port pinout Errors """""" If the red indicator light turns on, the system has exceeded the temperature cutoff threshold. While the red indicator is on the amplifier will be disabled. The amplifier will re-enable automatically once it has cooled down. If the error light turns on you should: - Wait for the light to turn off before attempting to use the amplifier again - Reduce your gradient pulse duty cycle (e.g. increase repetition time) Then, if the problem persists: - Check that the fans are still functional, you should hear them running as soon as the system is powered on - Ensure that the dust filters aren't clogged (see :ref:`hardware/gradient_amplifier:Maintenance`) Maintenance """""""""""" To ensure the module doesn’t begin to overheat, the dust filter should be cleaned regularly. To access the filter, ensure the module is powered off then remove the 4 screws on the panel on the under side of the module as seen below. The filters can then be removed, cleaned, and refitted. .. figure:: /images/peripherals/grad/dust_filter.jpg :width: 75% :align: center Dust filter cover removed .. note:: **Ensure filters and panels are refitted before the module is powered back on.**