Your task: To check the control circuits of items such as valve
actuators, motor drives, SCRs and heaters; manipulate test signals; and
analyze the results. So, you need a run-up box.
Wasn’t in the budget? Make one yourself.
It is a given that you already own a good digital multimeter and a clamp-on ammeter. You also need a run-up box. What's that? A little device that puts a 4 to 20 mA signal into the signal input of say, a control valve or SCR unit. It simulates the output signal of a controller or transmitter.